At least 22 wealthy party donors have been given jobs for life in the House of Lords over the past 13 years, an analysis has revealed.
Tory donors made up the largest group - with 15 party backers having been handed peerages during this period.
Billionaire businessman Michael Spencer became the latest wealthy donor to be ennobled on Friday, as Boris Johnson was accused of cronyism for stuffing the Lords with 19 new Tory peers, including his own brother Jo Johnson.
Downing Street insisted that the Prime Minister believes that the Lords should be shrunk in size - despite nominating 36 people in total, including Labour and non-affiliated peers.
But Mr Johnson was accused of u-turning on promises to slim down the upper chamber and swelling its ranks with cronies.
Analysis of the biggest donors over the past 13 years by the Financial Times found 22 donors had been made peers, donating some £50.4m to the main three parties either personally or through their related companies.
308 peers were created in the period, of which 15 were Tory donors, three were Labour benefactors and four were Liberal Democrats.
The majority of the cash came from Tory backing businessmen, including £3.5m from Stanley Fink, £8.2m from Anthony Bamford, £8.6m from Michael Farmer, £3.3m from James Lupton, £3.4m from Alexander Fraser and £2m from David Brownlow.
Mr Spencer, a former Conservative treasurer, has donated some £6m to the party’s coffers through his investment firm IPGL, the paper said.
Darren Hughes, chief executive of the Electoral Reform Society, said: “Pressure is mounting for an overhaul of the Lords, after this shocking batch of cronyistic appointments.
“Even the Lord Speaker recognises that this situation is untenable and has completely over-ridden even the Lords’ modest attempts at self-regulation.
“At over 800 members, this bloated chamber is making a mockery of democracy.”
It comes after Lord Speaker Norman Fowler criticised the number of new appointments and said the move encouraged peers who were “quite frankly passengers”.
Downing Street said new peers were needed to ensure the “appropriate expertise” but refused to comment on individual appointments, such as former cricketer Ian Botham and Russian-born newspaper owner Evgeny Lebedev.
The Prime Minister’s official spokesman said: “It remains the case that the size of the House of Lords needs addressing but given retirements and other departures some new members are needed to ensure the Lords has appropriate expertise and it continues to fulfil its role in scrutinising and revising legislation.”
The spokesman said it was a “long-standing convention that individuals can be nominated for an honour or peerage in recognition of their public and political service and that prime ministers can draw up dissolution and resignation lists”.
A Conservative party spokesperson told the FT: “Party donations do not play any part in the selection process. It is wrong to criticise individuals being honoured just because they have also chosen to donate to a political party.
“Donations should be transparent, but that is not an excuse to knock people for broader philanthropy, enterprise and public service.”
