Two former Conservative peers will defect to the United Kingdom Independence Party today, giving the Eurosceptic group its first foothold in Parliament.

Lord Pearson of Rannoch and Lord Willoughby de Broke will create a UKIP group in the House of Lords, promising to recruit other members and to persuade leading Conservative donors to switch allegiance.

The development is a severe blow for David Cameron, whose leadership faces mounting criticism for ditching traditional Conservative beliefs, with warnings from his own MPs that he is losing the support of core voters.

Nigel Farage, the leader of UKIP, said: “It’s an important step in UKIP’s development. To have a foothold in Westminster will make quite a difference. It means we have a voice inside the Westminster village, which has been badly needed. It will also help us raise money.”

Lord Pearson, who was put forward for his peerage by Margaret Thatcher, and Lord Willoughby de Broke, a former member of the House of Lords EU Scrutiny Committee, will enable UKIP to fulfil its long-held aspiration of a Westminster power base.

UKIP has ten members in the European Parliament, but has failed to get anyone elected to the House of Commons.

Several former MPs, including Roger Knapman and the television presenter Robert Kilroy-Silk, defected to UKIP, but only after they had left Parliament. Lord Pearson, chairman of PWS insurance broker, said that he was joining UKIP because Mr Cameron had softened his stance on Europe, particularly after a recent trip to Brussels, when he promised to work with the European Commission on tackling climate change.

He said: “We’ve really given up hope that under its present leadership the Conservative Party will be appropriately Eurosceptic by the next election. Under David Cameron, the leadership has become a lot more Europhile even than it was under Michael Howard,” he told The Times.

The two Lords took the Conservative whip for 15 years, but had it withdrawn in 2004 after they urged voters to support UKIP. They are now embarking on a full-scale defection, insisting that the interests of the country must be put before those of the Conservative Party.

Lord Willoughby de Broke, who is posting back his membership card to his local Conservative association, of which he is still a member, said: “This country’s best interests are served outside the European Union, and UKIP is the only party campaigning for that. Some will say we have let the Conservative Party down, but the party has let us down, and the country down.”

The peers hope that about half a dozen of their colleagues will follow their lead. Lord Pearson, who was offered a ministerial position by John Major, has been a leading party fundraiser. He is confident that donors will also make the switch. He said: “If you are a big funder of the Conservative Party, you are likely to be frustrated with the current leadership, and I know quite a few who are. I don’t see why people who have been funding the Conservative Party for a long time shouldn’t put their country before the current leadership.”

UKIP has been targeting disaffected Conservative supporters, recruiting several highprofile activists and former Tory candidates. However, the breakthrough into Parliament was possible only after UKIP dropped its previous pledge to destroy the Conservative Party. It recently said that it would not stand against any Tory MP officially supporting Britain’s withdrawal from the EU.

Last night the Plymouth branch of UKIP closed amid dissatisfaction at the way the party was run.

Tom Williams, the chairman of the branch, resigned at the annual meeting with eleven others, including three other officers and six committee members. He said after the meeting that he formally closed the branch because there were no nominations to take over from the officers.

Conservatives who moved on

Sir Oswald Mosley left the Tories to be independent in 1920. He joined Labour in 1924, and formed National Party in 1931

Sir Winston Churchill “ratted” from the Tories to the Liberals in 1904. He switched back in 1922

Source: Times database

Times Recommends

• Sarah Brown says 'no thanks' to veal at G8 - twice
• Stockton-on-Tees is obesity capital of Britain
• Stores blame poor sales on Murray factor