Iain Duncan Smith has been warned against allowing old allies from the Maastricht rebellions to exert growing influence on party policy towards the European Union.

The Conservative leader will on Thursday use a speech in Prague to make what his aides promise will be "a very major positioning speech about Europe".

A number of senior frontbenchers have privately expressed concern at the re-emergence of Bill Cash, the shadow attorney-general, and Tim Condon, a hard-line eurosceptic, in the drafting of the new stance.

One senior Conservative told today's Times: "Iain has done very well playing down the Europe issue since he became leader.

"But the row over the convention [on the EU constitution] has let this genie out of the bottle again. Surrounding himself with old cronies from the Maastricht rebellion does not help. In fact, I think we are in danger of playing into Tony Blair's hands."

Another frontbencher said: "We must resist the gravitational pull of this issue as well as the temptation of appealing to the editors of the Daily Mail and the Sun. Labour never got anywhere by concentrating just on its lead issues like health and education in the 1980s and we will get nowhere if we bang on about Europe."