IN THE mid-seventeenth century the chapel of the Spanish embassy caused considerable concern to the authorities at Whitehall since they were frustrated in preventing scores of Londoners from attending it for masses and other Catholic devotions. This was a distinct issue from the traditional right of a Catholic diplomat in England to provide mass for his household or other compatriots,’ and from the custom of Sephardic Jews to gather in the embassy for Sabbath worship when they desired. While the practice of Londoners to attend mass secretly at the residences of various Catholic diplomats had developed early in the reign of Elizabeth and occasional arrests at their doors had acted as a deterrent, late in the reign of James I sizeable crowds began to frequent the Spanish embassy. John Chamberlain commented in 1621 that Gondomar had ‘almost as many come to his mass’ in the chapel of Ely House as there were attending ‘the sermon at St. Andrewes (Holborn) over against him’. Although Godomar left in 1622 and subsequently the embassy was closed for five years during the Anglo-Spanish War, it was later, from 1630 to 1655, that the Spanish chapel acquired not only a continuous popularity among Catholics of the area but also an unwelcome notoriety in the highest levels of government. This paper will suggest two primary factors which led to that development: the persistent ambition of the resident Spanish diplomats to provide a range of religious services unprecedented in number and character, and their successful adaptation to the hostile political conditions in the capital for a quarter of a century. The continuous Spanish diplomatic presence in London for this long period was in itself both unexpected and unique for it should be recalled that, for various reasons, all the other Catholic ambassadors, whether from France, Venice, Portugal, Savoy or the Empire, had to leave at different times and close their chapels. However, the site of the Spanish residence during these years by no means permanent since, as with other foreign diplomats, a new property was rented by each ambassador on arrival. There is, moreover, a wider significance in this inquiry because of the current evidence that by the eve of the Civil War the king was considered in the House of Commons to have been remiss in guarding his kingdom from a ‘Catholic inspired plot against church and state’, for while it has been well argued that a public disquiet over Henrietta-Maria's chapels at Somerset House and St. James's palace had by 1640 stimulated increasing suspicions of a Popish Plot, there were other protected chapels, particularly the Spanish, where scores of Londoners were seen to attend. Indeed, after the closure of the queen's chapels at Whitehall in 1642, the Spanish remained for the next thirteen years as silent evidence that Catholics seemed to be ‘more numerous’ and were acting ‘more freely than in the past’.