See also William Yapp

In 1860 a congregation of Plymouth Brethren meeting in Orchard Street moved to No. 71, in conjunction with the transfer of the religious book and tract publisher William Yapp from New Cavendish Street to No. 70. Yapp, an early member of the Brethren, invented the floppy oversize cover known as a yapp binding, originally for pocket bibles. The Welbeck Street Assembly was not without social standing, its members including the 8th Earl of Cavan and the missionary 3rd Baron Radstock. ‘Welbeck Hall’, perhaps adapted from old manufacturing premises at the rear, continued in use for Brethren services and missionary meetings until 1909, when it was absorbed into the premises of J. R. Collett & Co., ball-gown makers at No. 72, the Brethren meeting subsequently in Great Portland Street.

https://www.ucl.ac.uk/bartlett/architecture/sites/bartlett/files/chapter14_welbeck_street.pdf