A Liberal Democrat MP today described the Tories as the enemy of his party as new evidence emerged about the concerns Lib Dem ministers have about their partners in the coalition government.

Adrian Sanders, the Lib Dem MP for Torbay, said that the Conservatives were the Lib Dems' natural opponents and that Nick Clegg should be talking more about the way he has managed to influence policy within the government.

The backbench MP spoke out as the Daily Telegraph published a fresh set of revelations about what Lib Dem ministers have been saying about their Tory colleagues to undercover reporters posing as concerned constituents.

Sanders, who raised his concerns in a post on his blog yesterday, told BBC Radio 4's Today programme this morning: "What is the point of being a separate political party if you don't consider that there are opponents to you? And the Conservative party is our opposition, in normal times."

When the presenter, James Naughtie, suggested that Sanders thought the Lib Dems were better off in coalition, because they were making a difference, even though the Tories were still their "enemy", Sanders replied: "Got it in one, Jim."

The MP went on: "Clearly, when we get to a national election, we will need to have a separate prospectus to put before people. But we are also going to have to explain to people what difference we have made from being in coalition. That is where we are falling down."

In his blogpost, Sanders wrote: "Unlike the bulk of the Liberal Democrat membership, the current leadership and their advisors are dominated by people who give the impression they didn't, among other things, enter politics to deny the Conservatives political power. That is the fundamental difference between them and those who have spent a lifetime campaigning against the enemy, and who view the Tories as the opposition to just about everything we stand for."

Today's Telegraph revelations show that Norman Baker, the Lib Dem transport minister, has likened his party's role in the coalition to that of moderates who fought the apartheid regime in South Africa from within the system. Baker compares himself to the late Helen Suzman, who fought apartheid as a member of the parliament that excluded black people.

Baker is one of four Lib Dem ministers featured in the Telegraph today, some of whom were recorded making disparaging remarks about David Cameron and George Osborne.

David Heath, the deputy leader of the Commons, said Osborne had the "capacity to get up one's nose". Paul Burstow, the care services minister, told the Telegraph's undercover reporters: "I don't want you to trust David Cameron."

The Telegraph also quotes critical remarks for the first time by a member of the four-strong Lib Dem team that negotiated the coalition agreement in May. Andrew Stunell, the local government minister, said: "I don't know where I [would] put him [the prime minister] on the sincerity monitor."

The remarks by Stunell, Heath and Burstow reflect the private thoughts of most Lib Dems. But Baker's decision to liken himself to an iconic Liberal in apartheid South Africa – indicating that he sees the Tories in a similar light to the National party of PW Botha – will raise eyebrows.

The transport minister said: "I always think in South African terms: should you be Nelson Mandela, outside the system, campaigning for it to be changed, or should you be Helen Suzman, who's my … one of my political heroes.

"Helen Suzman was in the apartheid regime when everybody was male and white and horrible actually. She got stuck in there in the South African parliament in the apartheid days as the only person there to oppose it. She stood up and championed that from inside.

"You do get your hands dirty by dealing with things you don't want to do, and sometimes you get results which aren't quite what you want. But the issue we have to make, the calculation in coalition, is we have to make as a coalition [sic] is do we get stuff that we do want which outweighs some of the stuff we don't want, and that's the reality of it."

Cameron, who visited South Africa in 1989 as the guest of anti-sanctions lobbyists, will not take kindly to being likened, however indirectly, to apartheid leaders. In 2006 Cameron visited Nelson Mandela to acknowledge his party's "mistakes" over South Africa when Margaret Thatcher led the fight against sanctions.

The disclosures in the Telegraph show Lib Dem ministers remain deeply suspicious of the prime minister and chancellor.

David Heath said of the millionaire chancellor: "George Osborne has a capacity to get up one's nose, doesn't he?" Heath added: "I mean, what I think is, some of them just have no experience of how ordinary people live, and that's what worries me."

Paul Burstow, who criticised the Guardian at the Lib Dem conference for attacking the coalition, told the Telegraph: "I don't want you to trust David Cameron … in the sense that you believe he's suddenly become a cuddly liberal. Well, he hasn't."