BRUSSELS — Prime Minister David Cameron on Friday pledged Britain will never become part of a “European superstate” thanks to a hard-fought deal for a less intrusive European Union which he hopes will sway voters in a referendum to keep the island nation in the 28-nation bloc.

The agreement Cameron won is a key stepping stone to the in-out referendum in Britain that could come as soon as this summer.

Cameron claimed that, under the deal, Britain would be allowed to stay on EU sidelines if other nations seek a closer union and has been guaranteed its social welfare would win more protection from unfair EU migrant claims. He also pledged the economy will prosper outside the euro area.

“This is enough for me to recommend that the United Kingdom remain in the European Union having the best of both worlds,” Cameron said after 31 hours of negotiations.

“Turning our back on Europe is no solution at all,” he said, adding that the new deal would guarantee for a “live and let live” approach which will fit Britain like a glove. He declined to say when he might call the referendum, although June 23 is thought a likely date.

EU President Donald Tusk said the deal didn’t come easy during two days of “long and heated” discussions during which leaders “haggled over detail” and fundamental issues.

Some said though, much was style over substance as all leaders needed to prove they would safeguard issues their electorate held dear. Still, Lithuanian President Dalia Grybauskaite said the deal should give the British public a clear choice.

“No matter what we do here, no matter what face-lifting or face-saving we perform here, it is up to the British people to decide,” she said.

Other leaders said it would not stop deeper integration among countries that want to, that the euro would remain the currency of the EU and that the agreement did not give Britain any veto.

The deal will only be enacted if Britain stays in the EU.

Outside the British Parliament in London, a leading anti-EU politician, Nigel Farage, took part in a rally denouncing the deal as it was announced.

“This is a truly pathetic deal,” he said. “We are good enough to be an independent, self-governing nation outside of the EU. This (referendum) is our golden opportunity.”

The summit in Brussels ran into overtime Friday as Cameron pushed his demands for more autonomy to the limit before a dinner among the 28 national leaders sealed the deal.

The deal offers guarantees to the nine EU countries, including Britain, that do not use the shared euro currency, that they will not be sidelined, and makes tweaks aimed at giving national parliaments more power.

Most of the tensions surrounded a relatively minor change: a move to suspend or restrict benefit payments made to workers from other EU countries.

Immigration is an especially sensitive point for British voters, because Britain has attracted hundreds of thousands of workers from Eastern Europe in the past decade, drawn by the prospect of higher-paying jobs. The EU immigrants can also claim child tax credits and other benefits in Britain, which Cameron’s government says is straining his budget.

Cameron also ran into unexpectedly firm resistance from France on financial regulation. French President Francois Hollande insisted Friday that Britain should not be given any “right of veto or blockage” and that all EU countries should have rules limiting speculation and avoiding new financial crises.

The 19 EU countries that share the euro currency worry that protections for Britain and the eight other non-eurozone nations would offer unfair advantage to Britain’s financial center, the City of London.

Hollande had also warned that too-generous concessions to Britain could prompt other countries to seek special rules, too.