A leading Liberal Democrat grassroots group has said that members are being left in the dark about how the party’s policies would be paid for.

In a briefing before the party’s spring conference in Liverpool this weekend, Liberal Reform described it as “regrettable that even at this final conference before the election, party members are being left in the dark as to how all of these plans are going to be funded”.

“The party is currently saying we want a 60:40 split between cuts and tax increases – that is tax rises of £30bn,” the briefing reads. “It is difficult to see how that can be funded without the basic income tax rate or VAT going up. And that is before the increases in spending to which the party is already committed.”

When asked about the comments at a press conference on Monday, deputy prime minister Nick Clegg said he had not heard of Liberal Reform, despite having written a forward to a major publication by the group in September 2013.

He said the party had a very democratic way of deciding policy, which set it apart from the “slightly more North Korean” approach taken by the other parties.

Clegg said: “I sat and participated all day on Saturday in the final meeting of the Liberal Democrat federal policy committee … a large group of federal Liberal Democrats elected to that body and elected to decide on behalf of the party what should go in our manifesto, which will then be subject to a vote this weekend.

“So I don’t know who you are alluding to, but the notion that somehow that is not done in an open, deliberate and consultative democratic manner is confounded by our meticulous adherence to the democratic ways we decide these things.”

Members of the three Lib Dem decision making committees are elected by its members, and party members who have been elected as local representatives then vote on the party’s policies at conferences.

Alan Muhammed, co-chair of Liberal Reform, said: “Our understanding is that some of the party committees have seen some costings relating to the manifesto proposals. However, many of those committees operate largely in secret and there seem to be no plans to give access to the figures to the wider membership.

“Yet it is the membership more broadly that is being asked to vote on these policies this weekend, without the benefit of seeing how much they will cost and how we propose to pay for them. This is unfortunate given that we rightly want to be seen as the party of sensible fiscal prudence.”

Liberal Reform adheres to the broadly pro-market, economically liberal ideology represented in the Orange Book, which was published in 2004 and co-edited by schools minister David Laws.

Liberal Reform’s 2013 publication, Coalition and Beyond: Liberal reforms for the decade ahead, included a foreword by Nick Clegg and chapters by care minister Norman Lamb, the Lib Dem spokesman for Northern Ireland Stephen Lloyd and communities minister Stephen Williams.