At the 1754 British general election, Bristow was returned as MP for Bere Alston again. He suffered great losses in the Lisbon Earthquake of 1755, which led to financial difficulties for him from then on. In November he and his partners were asked by the Treasury to procure provisions for Portugal, and in December Bristow and Burrell were appointed to provide money for the relief of those distressed in Portugal, and were to be paid £100,000 to cover costs. He became sub-governor of the South Sea Company in 1756. At the 1761 British general election, he was returned as MP for Arundel on the government interest. By this time he was owing the government considerable sums, but argued that his estate in Norfolk would provide more than enough to cover the amount, and he was owed large sums in Portugal. He went to Portugal and probably stayed there as he was absent for much of the parliament. He did not stand at the 1768 British general election.