Lyon Register has his name as James Loch.  But in his will it was transcribed to PCC records as Lock (no trailing ‘e’, so that has (in 2015) been dropped).

The history of the Morden Charity has him and a predecessor Sir John Lock as trustees of that charity.  At that time, the trustees were appointed by the Turkey Company and decided on the benefits to be received by failed merchants.

The implication is that James, and his predecessor Sir John were merchants of the Turkey Company, a monopoly that gave their members the additional benefit of freedom from customs duties on this trade.

I have yet to find any list of the various merchants of this Company.
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Found in an issue of The Derby Mercury Stated to be of 23rd April 1756 but carrying reports from the 27th (!) [the change to Gregorian calendars?] including this:

“This morning died suddenly, at his lodgings in Nicholas lane, Lombard Street, James Locke [sic], Esq; an eminent Turkey merchant, one of the Directors of the South-Sea Company, and one of the Trustees of Sir John Morden’s College on Blackheath.  He was a Gentleman greatly respected by all the knew him, and as much lamented by all his Friends and Acquaintance.[sic]”
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Brian Bouchard has found statements that his father was John Lock of Bristol and that he had these siblings:
1. Sir John Locke, Kt., East India Director, Sheriff of London 1726,
'eminent Turkey Merchant who resided at Ispadan in Persia, Will proved
18/11/1746,
2. Samuel Locke, Merchant of London, Will proved 7/1/1746 &
3. James
A daughter, Martha, married into the Rollinson family of Chadlington,
Oxfordshire. Her son Thomas Rollinson (James Lock's Exor.) became Sheriff of Oxfordshire in 1766. His Will was proved 7/2/1774

Lock or Locke is far too common a surname to confidently locate these.

Martha might be more hopeful and her son Thomas Rollinson was clearly named as a nephew and executor in James’ will.

And, indeed that marriage came up in St Luke’s, Old Charlton via FindMyPast:

First name(s)             Martha
Last name                 Lock
Marriage year             1740
Marriage date             19 Aug 1740
Marriage place            Saint Luke,Old Charlton,Kent,England
Spouse's first name(s)    Thomas
Spouse's last name        Rollinson
Parish                    Old Charlton
County                    Kent
Country                   England
Record set                England Marriages 1538-1973

Though this surprises me that they could have had a son Thomas old enough to be named an executor in James’ 1752 will.  Possibly ’nephew’ was used for ‘brother-in-law’?
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It now seems that Martha was a niece of James Lock as shown in this obit of Sir John from the London Evening Post of 8/11/1746: -

"Early on Thursday Morning died in an advanced Age, of an Apoplectick fit, at his Lodgings in King's arms Yard, Coleman Street, Sir John, Locke, ( who formerly resided many Years at Ispahan, the Capital of Persia) an eminent Turky Merchant of this City several Years in the Direction of the Hon. the East India and South Sea Companies, one of the Trustees of Morden's College on Blackheath, one of the Hon. the Court of Lieutenancy of this City, one of the Governors of St. Thomas's Hospital, and serv'd the Office of Sheriff of this City with Sir William Ogbourn during the Mayor- ley of Right Hon. Sir John Eyles Bart, in 1727. He has left one Daughter the Wife of Rawlinson, of Chipping Norton in the County of Oxford, Esq; who has several Children. He was a Gentleman that had a thorough Knowledge of Men and Trade, and died possess'd. of a plentiful Estate, which he acquired with great Reputation, and his Death is regretted by all who had the Pleasure of his Acquaintance."
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Dave Maddock has produced some superb research on the Loch family and identified them with the family reported in the Heraldic Visitation of London commenced in the year 1687, vol i, p, 43.  The published version of this Visitation even includes a note saying the John Locke the philosopher was of this family.  I will be entering up all that he has found on this family.

Dave also found that There are reports that James Lock had an earlier daughter, also Ann who in 1748 married a Mr Oates and has a dowry from James or £15,000.  It is thought that this Anne Lock was legitimate, particularly in view of her large dowry, but as yet the mother of Anne Oates née Lock is not known.

At marriage Anne Lock could have been 18 give or take a few years at marriage which would have made her born around 1730.  So if James married her mother, this would have been perhaps in 1728 give or take two years.  There are two marriages on FamilySearch of a James Lock at this time in the London and home counties region:

7 JUl 1726 at Westminster to Mary Brown.

22 July 1729 at Gillingham, Kent to Ann Teeling.

The images of both registers are said to be available and I hope to find if they give any more information.

Details are being added to the records of the persons concerned.
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His will was dated 19 June 1752 and proved at PCC on 4 May 1756 with Thomas Rollinson and James Harding as executors.