Adam Holloway, a Tory MP and member of the defence select committee, warned that Karzai's regime could not be trusted even if the payments could be justified on the grounds that Taleban and other insurgents must be rewarded if they give up the fight against Nato troops.
"Every effort towards a political fix in Afghanistan must be made and those efforts welcomed, but whether or not the money is well spent is a matter that must also be considered," he said. "There is plenty of evidence that Karzai and his clique do not have an interest in a peace settlement, but instead have an interest in continuing the conflict."
As Britain reduces troop numbers before withdrawing at the end of next year, there are fears that the pressure to seek a deal with insurgents will result in increasing amounts of secret cash being spent in Afghanistan.
"We also need to know more about how and where any cash from the UK is being used - how it is being monitored, and what benefits it is actually bringing to the people of Afghanistan," said Angus Robertson, the Scottish National Party MP and party defence spokesman.
"It is enormously important to ensure that Afghanistan is as peaceful as it can be in the build-up to withdrawal."
The revelation that Karzai's office is awash with cash from his allies has caused a furore in the Afghan Parliament where the Government has faced a barrage of corruption allegations.
"Accepting such money is a big insult to Afghanistan. All those who accepted the cash payments have betrayed the nation," said Hidayatullah Rihaee, an MP from Bamyan Province.
But Karzai said the cash flow was vital to his grip on power and said he had begged the CIA station chief to continue.
He admitted that the money had been passed on to potential allies, but added: "We have not spent it to strengthen a particular political movement. It has been given to individuals."