Prime Minister David Cameron said on Thursday he would veto any treaty to fix the European Union's debt crisis if it failed to protect the interests of Britain, in remarks aimed at reassuring eurosceptic members of his ruling Conservative party.

Cameron is under pressure to return from an EU summit aimed at rescuing the euro with something to reassure his restive right-wing, who see the current European crisis as a unique opportunity to reclaim powers from Brussels.

Speaking before leaving for the meeting in Brussels, Cameron said he would fight to win a good deal for Britain.

If I can't get what I want, I will have no hesitation in vetoing a treaty at 27 (EU members) because I am not going to go to Brussels and not stand up for our country, he said at an event in London.

That is what a prime minister should do and that is what I will do, he added.

Divisions over Europe tore apart the Conservative party last time it was in power in the 1990s and Cameron is painfully aware of how toxic the issue can be.

In Brussels Cameron will have to walk a fine line: he risks angering his own party if he backs measures to rescue the eurozone economy that involve ceding more powers to European institutions.

Legislators urged Cameron to ensure he at least wins adequate protection for Britain's financial services industry at the summit, in a letter published in Thursday's Conservative-supporting Daily Telegraph.

European Union proposals pose a grave threat to Britain's financial services industry, said the letter, signed by more than 20 Conservative members of parliament.

It is imperative that the government fights our corner by arguing either for a new EU protocol or a Britain-specific legal safeguard, it added.

Without strong action, the present drift seriously threatens both British jobs and Exchequer (tax) revenues, it added.

Cameron calls himself a eurosceptic but has stressed that the priority now must be rescuing the economies in the eurozone, Britain's biggest trading partner, playing down expectations he will be able to secure major concessions from Brussels.

He promised to secure safeguards for Britain's banking industry during a fractious session of parliament on Wednesday when members of his own party urged him to show some traditional British bulldog spirit at the summit.

Britain is the largest of the 10 countries that are part of the EU but are not in the single currency.

It is particularly concerned about Franco-German plans for a financial transactions tax which it says would hit London hard. Despite efforts to rebalance the British economy, financial services still account for more than 10 percent of the economy.

Cameron's position is made yet more difficult by the fact that he governs in coalition with the smaller, pro-Europe Liberal Democrats.

The prime minister has played down talk of a referendum on changes to the EU Treaty, disappointing party members who want Britons to have a vote to define their ties with the bloc. Britain joined in 1973 but has long had an ambivalent relationship with the rest of Europe and a distrust of deeper EU integration.

Northern Ireland Secretary Owen Paterson, a Conservative, added to Cameron's discomfort by saying that a referendum was inevitable if a more integrated eurozone was created.

This isn't going to happen immediately because these negotiations are going to take some months, Paterson told the Spectator magazine.

But I think down the road that is inevitable.

(Additional reporting by Tim Castle; Editing by Mark Trevelyan)