The disclosure follows PRWeek's revelations yesterday that the party is actively promoting its various ‘donor clubs', which offer differing levels of access to ministers and key aides.

An email sent out from Conservative Campaign Headquarters asks wealthy supporters to 'consider joining one of our donor clubs, which range from £2k up to £50k'.

A Conservative Party spokeswoman said today: ‘The Conservative Party has a very wide base of donors, around 2,000 of whom are members of these groups, which provide a structure for our supporters.'

The Conservatives risk accusations of cash for access by offering privileged access to certain groups, such as lobbyists. But the spokeswoman suggested the party was happy to accept lobbyists as members of all of the donor clubs.

She said: ‘Donors from a wide range of backgrounds are members of these clubs, including a small number of PR professionals. Details of donors are declared to the Electoral Commission as required.'

As revealed yesterday, members of the two most expensive donor clubs can attend ‘private presentations' with key figures including director of communications Andy Coulson and director of strategy Steve Hilton.

Members of the most expensive club, the £50,000-a-year Leader's Group, can attend lunches with Tory leader David Cameron after Prime Minister's Questions.