After opposing any concessions to Irish or English Catholics throughout his career, Sir Robert Peel, a Tory, supported the Duke of Wellington--who was also reluctant--Arthur Wellesley, the Prime Minister, in obtaining the votes to pass the Catholic Emancipation Act in 1829. As this website explains:
Support for the Anglican Church was the life-blood of Toryism. The Tories believed that there could be no yielding over the central rights of the Established Church. This therefore implied opposition to Catholic Emancipation on principle because it would destroy the constitutional supremacy of the Anglican Church. Canning supported Catholic Emancipation and wanted it to be passed before the repeal of the Test and Corporation Acts was granted. The Cabinet was divided on this however, so it was left as an open question and a settlement was deliberately postponed until the crisis of 1828-29.
Peel's Protestant convictions led to his refusal to join Canning's government in 1827 and Wellington refused to serve for the same reason, although he had been moving towards Catholic Emancipation since 1825 and personally had decided for it by the 1826 Irish General Election which demonstrated the electoral strength of the Irish Catholics. Wellington considered Catholic Emancipation to be a political, not a religious question. By 1828 he felt that resistance was impractical and dangerous because of the result of the County Clare election. . . .
He was crucial to the passage of Catholic Emancipation once it was clear that the "present position of Catholics in England" and Ireland was untenable:
In August 1828 after the County Clare election, Peel accepted the necessity for, but not the desirability of Catholic Emancipation. He tendered his resignation but Wellington persuaded him that the legislation would never pass without Peel's support. By January 1829 Peel's high-principled stand was weakening. He told Wellington that he would continue in office 'if my retirement should prove ... 'an insuperable obstacle' to the passing of Catholic Emancipation. Wellington responded:
"I tell you frankly that I do not see the smallest chance of getting the better of these difficulties if you should not continue in office."
Peel agreed to put Catholic Emancipation to the Commons. Only Peel and the Lord Chancellor were fully in Wellington's confidence over Catholic Emancipation. Peel put duty before principle and in February 1829 proposed the Bill to an astounded House of Commons. After all, for the past twenty years, Peel had been the one man who had consistently opposed the measure.
He was fiercely opposed in Oxford, whom he represented in the House of Commons, and lost his seat during an election in 1829. There was even a little verse about it:
You have altered your name from R. Peel to Repeal
In fact, we can see the effects of this election in Oxford today. When visiting Christ Church on the way to the Great Hall, the college website reminds visitors:
Before heading up the stairs be sure to note the markings on the doorway, especially the ‘No Peel’ graffiti. This was not a response to anything served up in the Hall - instead it was a protest at the potential re-election of Robert Peel, Christ Church alumnus and later prime minister, as the MP for the University. In 1829 Peel had announced his support for the emancipation of Catholics within Britain, though he had previously opposed such a move (Catholics at the time were barred from holding public positions). Peel knew that his volte-face conflicted with University policy and resigned his seat, but was promptly nominated to stand for re-election. The anti-Peel party set about making its feelings known in a divided Christ Church, nailing the door of the then treasury with the message ‘No Peel’. Due in part to their efforts, Peel was defeated in Oxford, but he returned to Westminster as MP for a small borough in Wiltshire. To this day, there is no picture of Peel within the Hall, even though he ranks among the most eminent of the college’s alumni.
Note that Mr. John Henry Newman, then a Fellow at Oriel College, was most supportive of opposition to Peel. While he was rather indifferent to the "Catholic cause" he was concerned that Emancipation would weaken the Anglican church, leading to "Indifferentism" in the Church of England. Find a sample of his letters during this period here.