m. (1) Joan Barmby, (2) Kathleen Turner.

I wonder if this was his birth?

Surname First name(s) District Vol  Page
Births Mar 1900
Quilter Denys Vaughan C Marylebone 1a 556

And this was his marriage in Q1 of 1940 on FindMyPast:

Quilter, Denys V C m. Turner Andover district vol 2c, p. 1023

So this defines his name!

Bridget remembers that he was known as Denys Cuthbert, so that probably solves what the ‘C’ stands for.  TFPL, July 2016: Confirmed from probate index.
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In the 1901 census he had three elder sisters and one elder brother in the house in New Hunstanton, Norfolk with a Governess-Housekeeper and four servants but no parents.  He was 1 and born in Paddington, London.  His siblings were:

Magdalen 9 Paddington, London
Gwendolen 8 Paddington, London
Lac’s (?) 6 Paddington, London
Gordon 3 Florence, Italy
Denys 1 Paddington, London

In 1911 he was at some institution (prep school presumably) in Thanet district of Kent, aged 11 and born in ‘Packington, London’.

But I cannot find any of his siblings in the 1911 census let alone any idication of his parents.  I must get gis birth certificate to find his parents.
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In 1939 he was at 92 Park St, St Albans:

Quilter Household (2 People)
92 Park Street , St Albans M.B., Hertfordshire, England

FIRST NAME(S) LAST NAME(S) DOB SEX OCCUPATION MARITAL STATUS  SCHEDULE  SCHEDULE SUB NUMBER

Denys V C Quilter 16 Nov 1899 Male Factory Manager Kapok Prod  Divorced  337  1
Mary Ross Murphy (Ross-Smith) 12 Apr 1903 Female Occupational Therapist  Single  337  2
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So he had been married before.  These records have been found from FindMyPast, for the banns, the church register and the public marriage index:

(a) Banns:

First name(s) Denys Vaughan Cuthbert
Last name Quilter
Banns year 1920
Banns date 14 Nov 1920
Place Sandgate, St Paul
Spouse's first name(s) Joan
Spouse's last name Barmby
Residence parish S Saviour St Georges Square London
Condition Bachelor
Spouse's residence parish Sandgate, St Paul
Spouse's condition Spinster
County Kent
Country England
Archive reference U3/277/1/C/1
Archive Canterbury Cathedral Archives
Record set Kent, Canterbury Archdeaconry Banns
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(b) Church register:

First name(s)           Deneys Vaughan Cuthbert
Last name               Quilter
Age                     21
Birth year              1899
Marriage year           1920
Parish                  St Saviour's, St George's Square, Pimlico
Spouse's first name(s)  Joan
Spouse's last name      Barmby
Spouse's age            25
Spouse's birth year     1895
County                  Middlesex
Country                 England
Archive                 City of Westminster Archives Centre
Record set              Westminster Marriages
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(c) Civil marriage index:

First name(s) DENYS V C
Last name QUILTER
Marriage quarter 4
Marriage year 1920
DENYS V C QUILTER married one of these people
Jean Barmby
Spouse's last name Barmby
District St. George Hanover Square
County London
Country England
Volume 1A
Page number 1173
Record set England & Wales Marriages 1837-2005
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No registration can be found for any children; there probably were none.
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From the probate index:

Quilter, Denys Vaughan Cuthbert of Malray Bell La Bircham Chichester died 6 January 1979 Probate Winchester 6 Feb £11628  793302033X.
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Their marriage:

Surname   First name(s)   Spouse   District   Vol  Page
Marriages Mar 1940   (>99%)
Quilter Denys V C Turner Andover 2c 1023
Turner Kathleen R Quilter Andover 2c 1023
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