Burrell was a very considerable merchant, a financier much consulted by the Treasury, and a steady Government supporter. Together with Thomas Walpole and the two Fonnereaus he held since 1752 a victualling contract for Gibraltar. In 1754, he was put up by Pelham
In 1761, after Grampound had placed itself under Edward Eliot and William Trevanion, Burrell was re-elected, presumably paying to the new patrons £2000 (as was done by Fanshawe).
Merrick Burrell apparently did not stand for Parliament in 1768—possibly he felt too old at 69. Nevertheless he succeeded William Burrell in May 1774 on the family interest at Haslemere, where he was re-elected after a contest at the general election in October. When present, he again supported the Government; but over the contractors bill, 12 Feb. 1779, he is listed by Robinson as ‘pro, absent’; and similarly he was absent from four out of six important divisions, between 3 Mar. 1779 and 24 Apr. 1780. By September 1780 the control of Haslemere had passed to Sir James Lowther, but Burrell secured his return for Great Bedwyn on Lord Ailesbury’s interest. In the new Parliament he is not known ever to have voted, either before or after the fall of the North Administration: ‘attends but little’, Robinson wrote about Burrell in his electoral survey of August 1782;
The victualling contract for Gibraltar was renewed to Burrell and Fonnereau in 1763 and 1765,
He died 6 Apr. 1787.
