John Major has added his name to calls for a referendum on any new constitution for the European Union.

The former prime minister, who pushed the Maastricht Treaty through the Commons without a national poll, said that Tony Blair should not abuse his parliamentary power to bring in constitutional changes over the public's head.

"It would be a tragedy if through lack of public awareness, the government were able to use its parliamentary majority to smuggle through crucial changes in our constitutional status without most of the British people understanding what has been committed in their name," Major wrote in the Spectator magazine on Thursday.

"Unless Mr Blair rejects many contentious proposals (or obtains significant opt-outs to protect our position), there must be a referendum here in the UK.''

The recommendations of former French president Valery Giscard d'Estaing's Convention on the Future of Europe had received little public attention until now, Major said.

"But they are bad. If unchanged (or unless rejected) they amount to a fundamental shift in the relationship between nation states and the EU and the shift of power is from the nation state," he argued.

"It is with sorrow and anguish that I read the likely conclusions of the convention.

"If they are not materially changed, or withdrawn, they threaten far greater damage to our national interest than premature entry into the euro."

The government has denied that the changes to accommodate 10 more members of the EU are any more radical than those introduced by Major in his time in Downing Street.

But while the Conservatives only ever held a slim Commons majority and had to rely on Ulster Unionist votes to ratify Maastricht, Major is concerned that Blair's overwhelming parliamentary power means he can force through changes with little scrutiny.

"I am uneasy that damaging concessions may be smuggled through the current parliament in lieu of the euro referendum that the government will duck," he said.

He accused his successor of hypocrisy in wanting a referendum on the single currency but not on the constitution, saying his arguments are "gibberish or an orator's trick to deceive".

"Upon an issue of this importance, the prime minister needs watching like a hawk," he said.

The convention does propose a transfer of sovereignty from Westminster to Brussels, Major claimed.

"The existing protection of a national veto largely disappears," he said

"We would be passing the fundamental control over the rules and safeguards of British liberty and justice to those outside our own democratic control."

The Liberal Democrats have joined the demand for a referendum from their own pro-European stance.

"We are in favour of a referendum if there are constitutional matters at issue," Liberal Democrat foreign affairs spokesman Michael Moore said.

"It is absolutely crazy to be ruling out a referendum at this stage,'' he told the BBC.

"Just as we were the first to call for a referendum on the single currency, we believe that it is important that where there are constitutional changes the British people should have their say."

However the government's representative on the convention, Welsh secretary Peter Hain, continued to argue that a referendum was not necessary.

"This is not an appropriate issue to put to a referendum," he said on Thursday.

"These kind of reforms of the EU's constitutional structure have always been dealt with by line-by-line examination in parliament."

"Parliament is the sovereign source of our whole constitutional authority in Britain and that is the right place to do it."