His baptism Transcript, by me:

“                   Page 115
“BAPTISMS solemnized in the Parish of St Pancras in the County of Middlesex in the Year On Thousand eight Hundred and Fourteen
“. . . .
“When Baptized:      March 21st
“No:                 924
“Child’s Name:       John George son of
“Parents forenames:  Donald and Jean
“Parents Surname:    MacLean
“Abode               Brunswick Square
“Profession:         Gentleman
“Celebrant:          Robert Mayne, Rector of Limpsfield, Surrey
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There are three John George Maclean marriages on Findmypast, in 1845, 1859 and 1890, though the last is, of course after his death.  My guess is that the first is his, but some facts are needed.  Let’s have a look at the 1851 census first:

But he and his family could not be found in 1851 and 1861, even though all the children were born in England, from the 1871 census.  Perhaps he was a broad and I need to search for a house with his wife and a child or two in 1851 and 1861?
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In 1851 they were at Wimpole Street but the surname was recorded as ‘McLean’; they had three children with them:

First name(s)  Last name  Relationship  Marital status  Sex  Age  Birth year  Occupation  Birth place
George J   McLean   Head      Married    Male    37  1814  General Merchant  St Pancras, Middlesex
Henrietta  McLean   Wife      Married    Female  24  1827  -                 Gloucester, Glos
George H   McLean   Son       -          Male     3  1848  At Home           Marylebone, Middlesex
Henrietta  McLean   Daughter  -          Female   2  1849  At Home           Marylebone, Middlesex
Emily A    McLean   Daughter  -          Female   1  1850  At Home           Marylebone, Middlesex
Francis    Signale  Servant   Unmarried  Male    31  1820  Butler            France
Susannah   Wilson   Servant   Unmarried  Female  25  1826  Cook              Marylebone, Middlesex
Catharine  Suton    Servant   Unmarried  Female  29  1822  Housemaid         Chichester, Sussex
Georgina   Aitken   Servant   Unmarried  Female  25  1826  Nurse Maid        Scotland  
Emily      Somers   Servant   Unmarried  Female  19  1832  Nurse Maid        Gloucestershire

Ref:
Series         HO107
Piece number   1487
Folio          137
Page           18
Combined:      HO107, piece 1487, folio 137, p. 18
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This revealed that in 1861 John George was in England, with his family but given a birth year of 1824 instead of the 1814 I had searched for.  They were living at 130 Westbourne Terrace, Paddington:

First name(s)  Last name  Relationship  Marital status  Sex  Age  Birth year  Occupation  Birth place
John G       Maclean  Head      Married    Male     37  1824  General Merch  St Pancras, Middlesex
Henrietta C  Maclean  Wife      Married    Female   34  1827  -              Gloucester, Glos
George H   Maclean  Son       -        Male     13  1848  Scholar        Marylebone, Middlesex
Donald H D   Maclean  Son       -          Male      8  1853  Scholar        Marylebone, Middlesex
Norman       Maclean  Son       -          Male      7  1854  Scholar        Paddington, Middlesex
Gerald A     Maclean  Son       -          Male      3  1858  -              Paddington, Middlesex
Arthur J     Maclean  Son       -          Male      3  1858  -              Paddington, Middlesex
Rose B       Maclean  Daughter  -          Female    1  1860  -              Paddington, Middlesex
Charles L    Maclean  Son       -          Male      0  1861  -              Paddington, Middlesex
Henry        Hartey   Servant   Married    Male     36  1825  Butler         Marylebone, Middlesex
Jane         Batt     Servant   Married    Male     39  1822  Nurse          Gosford, Hampshire
Emma H       Hallows  Servant   Married    Female   22  1839  Under Nurse    Horton, Middlesex
Esther       Parr     Servant   Married    Female   22  1839  Nursery Maid   Poplar, Middlesex
Ann          Newby    Servant   Widow      Female   36  1825  Cook           Hanground, Northants
Sarah J       Sweet    Servant   Unmarried  Female   29  1832  Housemaid      Hallifax, Nova Scotia

Ref:
Archive reference  RG09
Piece number       11
Folio              95
Page               7
Combined:          RG09, piece 11, folio 95, p. 7
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In 1871 he was at Westbourne Terrace, Paddington, Kensington, London & Middlesex with the two sons who became his executors in 1879:

First name(s)  Last name  Relationship  Marital status  Sex  Age  Birth year  Occupation  Birth place
John G       Maclean    Head      -  Male    57  1814  East India & American Mercht  London, Middlesex
Henrietta C  Maclean    Wife      -  Female  44  1827  -                             Gloucestershire
George H     Maclean    Son       -  Male    23  1848  Merchant’s Clerk              London, Middlesex
Donald F D   Maclean    Son       -  Male    18  1853  Merchant’s Clerk              London, Middlesex
Rose B       Maclean    Daughter  -  Female  11  1860  -                             London, Middlesex
Henry        Elmer      Servant   -  Male    58  1813  Butler                        London, Middlesex
William      Cook       Servant   -  Male    17  1854  Footman                       W Peckham, Kent
Elizabeth J  Ellis      Servant   -  Female  45  1826  Cook & Housekeeper            Chatham, Kent  
Elizabeth A  Russell    Servant   -  Female  37  1834  Lady’s Maid                   Dover, Kent
Jane         Baldwin    Servant   -  Female  31  1840  Housemaid                     Gaucott(?), Bucks
Amelia       Reed       Servant   -  Female  20  1851  Under housemaid               London, Middlesex
Emma E       Causbrook  Servant   -  Female  25  1846  Kitchen maid                  Leics, Northants

Ref:
Archive reference  RG10
Piece number       25
Folio              50
Page               51
Combines:          RG10, piece 25, folio 50, p. 51

This confirms that his wife was Henrietta Caroline Wilton whom he married in 1845.
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The following Maclean births were found on Find My past with a Wilton mother:

Last name  First name(s)  Year Of Birth  Year Of Death  Year  Location   On GRO   Bapt HC
Maclean    Florence Georgina  1846  —  1846  St. Pancras, London            Y       Y
Maclean    George Henry       1847  —  1847  Marylebone, London             Y      (tr)
Maclean    Henrietta Marian   1849  —  1849  Marylebone, London             Y       Y
Maclean    Arthur James       1857  —  1857  Kensington, London             Y
Maclean    Gerald Alexander   1857  —  1857  Kensington, London             Y
Maclean    Gaspard            1858  —  1858  Kensington, London             Y       Y
Maclean    Rose Beatrice      1860  —  1860  Kensington, London             Y       Y
Maclean    Charles Lionel     1861  —  1861  Kensington, London             Y      (tr)

This omits Donald Frederick Durant who was one of his father’s executors.  Possibly his mother’s name has not yet got onto FindMyPast’s records.

But Donald F D’s birth was found as a baptism, only, on Ancestry, with image.

A check on the new GRO database adds:

Name:                 Mother's Maiden Surname:
MACLEAN, NORMAN       WILTON  
GRO Reference: 1854  J Quarter in KENSINGTON PADDINGTON AND FULHAM  Volume 01A  Page 32

And Norman is now found on the 1861 census.  And his baptism image has been found.
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His death index:

First name(s)   John George
Last name       Maclean
Gender          Male
Birth year      1814
Age             65
Death quarter   1
Death year      1879
District        Kensington
County          London
Volume          1A
Page            52
Country         England
Record set      England & Wales Deaths 1837-2007
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His probable proaabate index:

MACLEAN John George Esq.
260
Personal Estate under £90,000.
20 March  [1q879].  The Will with two codicils of John George Maclean formerly of Charlwood Park Charlwood in the County of Surrey but late of 130 Westbourne-terrace Hyde Park in the County of Middlesex Esquire who died 2 February 1879 at 130 Westbourne-terrace was proved at the Principal Registry by George Henry Maclean and Donald Frederick Durant Maclean both of 130 Westbourne-terrace Esquires the Sons two of the surviving Executors.
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Their marriage index:

First name(s)     John George
Last name         Maclean
Marriage quarter  3
Marriage year     1845
MarriageFinder    John George Maclean married one of these people
                  Henrietta Caroline Wilton, Elizabeth Hatherall
District          Stroud
County            Gloucestershire
Country           England
Volume            11
Page number       561
Record set        England & Wales Marriages 1837-2005
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Their Licence to marry from the Faculty Office:

First name(s)          John George
Last name              Maclean
Licence year           1845
Licence date           12 Jul 1845
New calender date      12 Jul 1845
Bride's first name(s)  Henrietta Caroline
Bride's last name      WILTON
Groom's first name(s)  John George
Groom's last name      MACLEAN
Place                  Dioceses of England & Wales
Record set             Faculty Office Marriage Licences
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Finally, Ancestry has an image of the parish register, trancript by me:

[  Painswick  >  1845  ]

1845 MARRIAGE solemnized at the Parish Church in the Parish of Painswick in the County of Gloucester

No:                     112
When married            July 22
                          His                        Hers
Name and Surname:       John George MacLean        Henrietta Caroline Wilton
Age                     Of full age  31            Minor
Condition:              Bachelor                   Spinster
Profession              Merchant
Residence at Marriage:  London                     Painswick
Father                  Donald MacLean             Robert Wilton
Father’s profession:    Merchant                   Solicitor

Married in the parish Church according to the Rites and Ceremonies of the Established Church by Law by me: Thomas Evans D.D.
The Marriage was solemnised between us: [signed] John George Maclean, Henrietta Caroline Wilton
In the Presence of us: Robt Wilton, D Maclean, Jean Maclean, Francis Mary Wilton, J W Wilton
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