Sadly, no figures for Catholic apostasy have survived for England as comparable with the convert rolls of Ireland, so it is impossible to give an exact number of apostates in this period. Certainly, no official record of Sir Thomas's apostasy was kept by Lambeth Palace. However, one thing is certain: apostasy among the English Catholic gentry in the late eighteenth century was not uncommon. Contemporary Catholic observers were concerned by what they perceived to be a great qualitative decrease of English Catholic gentry and they regarded apostasy as ‘a major and catastrophic cause of the decline’.

Conformity to the established religion was rewarded with social advantages and so was a great temptation for gentlemen outside the Anglican fold who wished to follow a career in government service or in Parliament. In almost every county in England many heads of old English Catholic families conformed. In the West Riding alone, of the twenty-four Catholic gentry families that existed in 1706 only twelve remained by 1780. Between the years 1754 and 1790 at least eight members of the House of Commons had renounced Roman Catholicism in order to pursue political careers and, according to the contemporary Catholic priest Joseph Berington, by 1780 there were but 177 landed Catholic families in England, ten of which had either died out or recently abjured their faith.

Berington's concerns were well justified. Just a few conversions could have devastating consequences for Catholic communities. As David Butler points out, often ‘Catholic missions were over-dependent on the Catholic aristocracy and gentry for the continuance of Catholic worship’ and, for Butler, in eighteenth-century London alone, if ‘just eight prominent families had apostatised … the Catholic missions would have lost about half of their numbers’.

Despite this, and with seemingly little regard for the consequences it might have on the Catholic community resident on his estates, Gascoigne abjured his faith within months of returning to England following his Grand Tour. Initially, Gascoigne was due to travel back to Italy with Henry Swinburne in February 1780 but, upon deciding to settle in Parlington and retrench his expenditure, the idea that he might conform was beginning to take shape. Upon returning to Britain he seems to have craved the ‘consequence’ he had achieved on the Continent and had been brought up by his guardians to expect.