"And yes, we will deliver that in/out referendum on our future in Europe," Cameron said in his victory speech.
The UK general election was held on May 7. The Conservative party managed to secure 328 seats in the vote, as last British constituencies are declaring their results.
The UK membership in the European Union has become one of the most hotly-discussed topics in the run-up to the vote. Cameron's Tory party pledged to hold a EU membership referendum in 2017.