NICK Clegg was branded "untrustworthy" by Tory MPs last night after a close aide suggested the Liberal Democrats could block plans for a constituency boundaries shake-up in tit-for-tat move.

Richard Reeves, in a parting shot as he left his job as the Deputy Prime Minister's director of strategy, made it clear this week that there would be "consequences" if the Conservatives sought next week to derail plans for House of Lords reform.

Describing next Tuesday's key Commons vote on the Lords Reform Bill as "hugely significant," Mr Reeves declared: "The idea that failure to deliver a government commitment on Lords reform would be consequence-free is for the birds."

Tory MPs have insisted the deal between the two parts of the Coalition was that in return for giving the LibDems a referendum on the Alternative Vote, the Conservatives would see a review of constituency boundaries.

Experts say the review could give the Tories 20 extra seats in the 2015 General Election.

However, Mr Reeves and other LibDems have clearly linked the review to Lords reform.

On Tuesday, MPs will vote on a motion that sets out the Government's proposal to limit the time spent debating the Lords plans, which would halve the second chamber to 450 senators, 80% of them elected.

Prime Minister David Cameron has made it clear that ministers or parliamentary aides who defy the Government three-line whip will be sacked.

But Eleanor Laing, the Conservative MP for Epping Forest, said she intended to vote against the Government: "On constitutional matters, votes done can't be undone and changing our whole system of government is too important a matter to be rushed through the Commons."

She added: "When I asked Nick Clegg only a few weeks ago if there was a link between boundaries legislation and Lords legislation he said: 'Of course, there's no link.' So how unfortunate if his words can't be trusted."

Fellow Tory MP Peter Bone also insisted the Coalition deal on the constitution did not extend to Lords reform. Referring to the LibDems, he said: "They just can't be trusted," and added: "The Liberals messing around like this just proves the sooner we get to a minority Conservative Government, the better."

Tory backbencher Chris Heaton-Harris tweeted: "Can't get my juices flowing over Lord's reform. One thing, however, might make me rebel – LibDem blackmail."