Catholic peers were excluded from the House of Lords from 1 December 1678 unless they apostasised - statute 30 Car II st 2 (1678) "An Act for the more effectuall preserving the Kings Person and Government by disableing Papists from sitting in either House of Parlyament". The Act required peers (and MP's) to take the Oaths of Allegiance and Supremacy and make a declaration abjuring Transubstantiation, Invocation of Saints and the Sacrifice of the Mass by that date, failure to do so meant exclusion from the House and future peers and MP's had to take the oaths and make the declaration of abjuration before taking their seats. The Duke of York (the future James II and VII) was excluded from the terms of the Act.
The Roman Catholic Relief Act 1829 repealed the provision requiring the declaration to be made by peers, MP's (and others) and permitting Catholic peers and MP's to make, instead of the Oaths of Allegiance, Supremacy and Abjuration, an oath of simple allegiance, to defend the King, to disclose treasons against him, to maintain the Protestant and Hanoverian succession to the Crown, to renounce any obedience to pretenders and to declare that it was not an Article of his faith that princes excommunicated or deprived by the Pope may be murdered or deposed, or that the Pope of foreign princes have temporal or civil jurisdiction within the Realm. They also had to swear to defend the the settlement of property within the realm, abjure any intention to to subvert the established Church and to swear not to disturb or weaken the Protestant religion or government in the UK. The Act came into effect on 23 April 1829