John Swinney addressing the conference

Leader John Swinney says his party cannot support the plans because they will "entrench" Brussels' control of fishing policy.

The SNP claims the Common Fisheries Policy is destroying the Scottish industry.

But Scottish Executive officials denied Brussels would be handed exclusive power over fisheries under the change.

The SNP tends to adopt a pro-European stance.

However, Mr Swinney said that the party could not support the proposed European constitution if control over fishing remained exclusively with Brussels.

The new rules will underpin the EU as more countries join.

UK Prime Minister Tony Blair has insisted that he will not accede to demands for a referendum on the draft constitution.

Every country in Europe is seeking amendments to the constitution on the basis of their individual national interest - that does not make them anti-Europeans John Swinney SNP leader

He has also promised that the UK will not allow it to diminish British sovereignty over the "red lines" of tax, defence and foreign policy.

Mr Swinney believes it is now "inevitable" that the rulebook - being finalised by member state governments in the next few weeks - will enshrine Brussels control of Scotland's fisheries.

He announced the move in a keynote speech to the party's national council in Glasgow on Saturday.

The Nationalist leader insisted that the policy of opposing the constitution does not diminish the SNP's "pro-Europe and pro-EU position".

He said: "In two weeks time the 15 full members of Europe will once again decide Scotland's fishing policy.

Destroyed livelihoods

"Tiny land-locked Luxembourg will have a vote on the future of Scottish fishing, while Scotland is locked outside. No other country would put up with such a nonsense. Neither should we.

"We need an independent voice in Europe to put an end to the disastrous Common Fisheries Policy which has cost jobs, destroyed livelihoods and hammered Scotland more than any other European country.

"And were we an independent nation, the opportunity to change this would be available today - available because the European Constitution is up for negotiation.

"That constitution currently proposes to entrench exclusive EU control over fishing and an Independent Scottish Government would veto that proposal.

The new rules aim to underpin the EU as more countries join

"But we don't have independence so the only choice open to us is to campaign against the whole constitution.

"The SNP cannot, and will not, support the proposed European Constitution if control over fishing remains exclusively with Brussels."

He added: "Every country in Europe is seeking amendments to the constitution on the basis of their individual national interest. That does not make them anti-Europeans.

"On the contrary it makes them full, normal and enthusiastic participants in the European process. But that choice isn't open to Scotland, therefore, we must fight with the weapons we have available to us and we must say `no' to the new EU Constitution."

Mr Swinney also used Saturday's meeting to attack Scottish Labour MPs for refusing to take a public stand against top-up university tuition fees for English universities.

Nationalists claim top-up fees will be disastrous for Scottish universities who could lose academic talent to better-funded English institutions.

The SNP has endorse tentative moves towards joining a "convention" of pro-independence parties.

'Little surprise'

The idea was first publicly floated in September but was opposed by some senior Nationalists on the grounds that it could give voters to green light to vote for the party's political enemies.

But Mr Swinney is said to be "relaxed" about the idea.

A spokesman for the executive said: "The conservation of the marine environment is a matter of shared concern.

"The draft constitution makes clear that while the conservation of marine biological reserves will be an exclusive European competence, fisheries management will be shared as it always has been."

But a senior spokesman for Scottish Labour said Mr Swinney's announcement came as little surprise.

"This is yet more proof of the SNP's slide into euroscepticism," he added.