to prevent it becoming too powerful, any regional assembly elected in the North-East will have only 25 members, a Government minister admitted yesterday.

Nick Raynsford surprised MPs when he revealed that the assembly would be kept small so it could not "trample on local authorities or try to usurp their functions".

The Local Government Minister said: "If you keep the assembly small, it is much less likely to start looking for extra work to undertake and start trampling on local authorities.

"If you have a large assembly, there will inevitably be tensions between the different tiers of government.

"Elected regional assemblies should focus on regional matters.

"They should not interfere with the work of local authorities and shouldn't be double guessing the work of Members of Parliament."

Mr Raynsford's comments, to a committee of MPs, will be powerful ammunition to the No campaign, which has argued the assembly will be a toothless "talking shop".

They came just a day after the chairman of the unelected North East assembly told the same committee that the elected body should have a membership of 45.

Councillor Bob Gibson said an assembly of 25 would be too small to carry out its responsibilities effectively, or serve constituents properly.

But Mr Raynsford insisted a 25-strong body had worked well in London, where the assembly had not "tried to double guess or duplicate the work of local authorities".

Mr Raynsford said the Government would introduce extra clauses to "define local authority functions which will be off limits for elected regional assemblies".

Yesterday, the Yes campaign stole a march by appearing before the MPs' committee to give evidence to its inquiry - an invitation the No campaign failed to take up.

Spokesman Alan Donnelly, a former MEP, said: "I find it astonishing that the No campaign failed to turn up, given that it claims to represent the people of the North-East and says it wants to debate the facts."