Prime Minister David Cameron pledged to investigate why a senior Conservative party fundraiser offered exclusive access to him in return for donations of 396,700 dollars a year.
Cameron said the actions of co-treasurer Peter Cruddas, caught on film by undercover reporters, had been completely unacceptable, as he sought to limit the damage to his centre-right party.
Cruddas resigned soon after the Sunday Times newspaper published video of him telling journalists posing as international financiers that the contributions would enable them to have input into public policy and ask Cameron practically any question you want.
The affair threatens to undo Cameron's efforts to shake off his party's image of being too close to the interests of business and the rich as Britain undergoes an austerity programme to cut its budget deficit.
This is not the way that we raise money in the Conservative party, it should not have happened, said Cameron. I will make sure that there is a proper party inquiry to make sure this can't happen again.
The disclosures capped a torrid week for the Conservative-led coalition government after a backlash over a budget that cut tax rates for top earners while freezing tax allowances for pensioners.
While there were also tax cuts for lower earners, the budget went down badly with many Britons, giving the impression the government was looking after the wealthy and cared little for those suffering rising unemployment and falling incomes as the economy struggles to recover from recession.
The funding issue is embarrassing for Cameron, who promised before coming to power in May 2010 to curb corporate lobbying, saying it was the next big scandal waiting to happen.
The revelations were utterly disgraceful, Treasury Minister Danny Alexander, a senior member of Cameron's Liberal Democrat coalition partners, told BBC TV.
The opposition Labour party called for an independent inquiry into what access had been sought and obtained, and demanded Cameron make a statement about the affair to parliament.
It can't just be an internal Conservative party investigation sweeping it under the carpet, said Labour leader Ed Miliband.
This is very serious for our democracy because we need to have the highest standards in our public life. And what we have seen today falls way below the standards that British people have a right to expect, Miliband added.
The disclosures will add urgency to talks between all three main parties in coming weeks on reform of political funding. Previous reform attempts have foundered on the Conservatives' reluctance to cap donations from wealthy individuals and Labour's desire to avoid limits on contributions from unions.