Britain's ruling Conservative party is ralllying for re-election in 2015 at its ongoing party conference, overshadowed by defections to the eurosceptic UKIP and a ministerial resignation over a sex scandal.

Prime Minister David Cameron admitted there had "not been an ideal start" on Sunday to the gathering in Birmingham, after a lawmaker defected to join the eurosceptic UK Independence Party, and a minister resigned for sending explicit photos.

The defection of lawmaker Mark Reckless to UKIP on the eve of the conference -- the second MP to do so in two months -- upped the pressure on Cameron to harden his stance towards the European Union and immigration.

The prime minister told BBC news he would support whatever was in the country's interest.

"If I thought that it wasn't in Britain's interests to be in the EU I wouldn't argue for us to be in it," Cameron said.

The centre-right Conservatives, who currently govern in coalition with the smaller Liberal Democrats, risk losing a handful of seats and thousands of votes to UKIP at next May's general election -- possibly enough to cost them victory.

In a bid to seize back momentum, Finance Minister George Osborne on Monday unveiled plans to abolish an inheritance tax on pensions before the election.

The decision to scrap the 55 percent tax on pension pots when they are passed to children and grandchildren was reported to affect hundreds of thousands of people and £150 million a year ($244 million, 192 million euros) in tax revenues.

Osborne is expected to make a speech later Monday arguing that only his party can strengthen the economy.

While polls have consistently put the main opposition Labour party several points ahead, they have also shown the Conservatives are more trusted to deliver economic growth after overseeing a recovery.

But a ComRes survey released Monday indicated the party could face an uphill struggle to win outright victory, giving Labour a convincing lead in crucial marginal seats.

Cameron has vowed to re-negotiate the terms of Britain's membership of the EU and hold a referendum on whether to leave the bloc by the end of 2017 in a bid to ward off UKIP gains and appease the eurosceptic wing of his party.

The prime minister described Reckless' defection as "frustrating... counter-productive and rather senseless" after the lawmaker announced he was leaving out of frustration with Conservative policy on immigration and the EU.

UKIP leader Nigel Farage has hinted at more defections to come, and the conference comes a week before a by-election which could see UKIP land its first seat in the House of Commons at the Conservatives' expense.

Douglas Carswell, a Tory MP who switched sides to UKIP in August, is expected to be re-elected in the coastal town of Clacton, southeast England, on October 9, threatening a major embarrassment for Cameron.

Europe has long been an open wound for the Tories, with many rank and file members wanting to leave the EU altogether, and on Sunday a senior Conservative minister Sajid Javid said that going it alone would "open up opportunities" for Britain.

Within hours of Reckless defecting, civil society minister Brooks Newmark, a 56-year-old married father of five, was exposed in the Sunday Mirror newspaper for sending a graphic image of himself to an undercover male journalist posing as a young PR girl called Sophie.

After stepping down as minister, he told ITV television he had been a "complete fool".

The events overshadowed promises by the prime minister of discounted homes for younger buyers and fresh cuts to social welfare, and a debate about the constitutional future of the United Kingdom also hovered over the event.

The conference opened with a debate on the state of the UK, shaken by a referendum that saw Scotland reject independence in a closely-fought race.

Scots were promised greater powers over tax, spending and welfare in return for rejecting independence, opening a debate about whether more powers should be devolved from London to Northern Ireland, Wales, and other regions of England.

Speaking at the conference, Northern Ireland secretary Theresa Villiers announced that Britain and Ireland would revive talks between nationalist and unionist parties to solve a standoff that has threatened the fragile power-sharing Belfast administration.

Disagreement over Westminster welfare reforms has compounded differences between the mainly Protestant unionists and mostly Catholic nationalists, who are starkly divided on issues from parades to dealing with the region's troubled past.

Still to come at the conference is Cameron's keynote speech on Wednesday, in which he will set out his pitch to be re-elected prime minister.

Also closely watched will be a Tuesday address by London Mayor Boris Johnson, who is bidding for election to parliament next year, and is seen as Cameron's potential successor.