The elected assembly will have just 25 members to prevent it becoming too powerful, a government minister admitted today.

Nick Raynsford surprised MPs by revealing the North-East assembly would be small specifically 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 shouldn't 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 one 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 warned that a 25-strong assembly 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 - a city of 7m people - where the assembly had not "tried to double guess or duplicate the work of local authorities".

The minister also poured cold water on the hopes of the 'Yes' campaign that the assembly, once established, would quickly win additional powers from London.

He said: "I believe there is a coherent and good package of powers contained in the Bill which will give elected regional assemblies plenty to get on with in their early years.

"I certainly wouldn't envisage any immediate changes beyond the packages which will be put to parliament when we introduce the Bill."

Furthermore, Mr Raynsford added, the government would introduce extra clauses to "define local authority functions which will be off limits for elected regional assemblies".

The 'Yes' campaign stole a march by appearing to give evidence to the committee's inquiry yesterday - 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."