A SENIOR aide to Deputy Prime Minister Nick Clegg has warned the Conservatives risk damaging their own electoral fortunes if they block his flagship plan for Lords reform.

Richard Reeves, who yesterday stood down as Mr Clegg's director of strategy, said the party is in for a "rude awakening" if it tries to prevent the reforms.

LibDems are expected to halt boundary changes that could boost Tory chances at the next General Election if a deal struck at the start of the Coalition is reneged on.

The pact allows Tories to secure a shake-up in the constituency boundaries, which experts believe will benefit them by up to 20 seats in 2015; while the LibDems would get their reform of the Lords.

Next week, MPs will vote on a motion to limit the amount of time debating the Lords Reform Bill, which would halve the number of members of the second chamber to 450 with 80% elected.

As many as 100 Tory right wingers, however, have threatened to join Labour and vote against the timetable motion. If defeated, it could lead to the debate dragging on for months with the prospect of the Bill eventually being killed off.

Mr Reeves said: "The idea that failure to deliver a Government commitment on Lords reform would be consequence-free is for the birds."

Stressing a "deal is a deal", he added: "Anyone who thinks Nick Clegg will shrug his shoulders [after a defeat], say 'never mind' and 'everyone tried our best', will be in for a rude awakening."