The failure to fulfil Pitt's pledge on emancipation – under which Catholics would be able to sit in Parliament – also weakened the union almost from its birth.
The issue was kept alive by Henry Grattan, who returned to politics as MP for the English constituency of Malton, then from 1806-20 as one of the Members for the city of Dublin.
In May 1808 Grattan proposed emancipation in the House of Commons, with certain qualifications, but his motion was defeated by 281 votes to 128.
In June 1812 the Commons accepted, by 225 votes to 106, a motion in favour of considering Catholic claims.
An emancipation Bill, introduced in February 1813, received a second reading but was lost in committee by a narrow margin.
Frustration at this lack of progress led to the formation of the Catholic Association in 1823. Parliament passed an Act to restrict the Association's activities two years later.
The election of Daniel O'Connell in Clare - although as a Catholic he initially could not take his seat - proved decisive.
The House of Commons and the Cabinet were now convinced that action was necessary and the King's Speech of February 1829 included a promise of Catholic relief.
A Bill was introduced in the Commons a month later. It passed through both Houses of Parliament with little trouble and received Royal Assent in April.