LONDON, May 8  -- David Cameron, British Prime Minister and leader of the Conservative Party, Friday confirmed his promise on holding the in-out European Unionreferendum.

Delivering a speech outside 10 Downing Street after visiting Buckingham Palace, he said he will lead a government for "one nation" and will make "Great Britain greater", after the party win the 2015 General Election with more than half seats of the House of Commons.

"Yes, we will deliver that in-out referendum on our future in Europe," Cameron said.

He also pledged to move as fast as possible with a plan to give more powers to Scotland, where the Scottish National Party (SNP) won an overwhelming majority of seats this time.

According to the results from individual constituencies that released at 1340 local time, the Conservatives have already locked 328 seats in the Commons, while SNP has won 56. Three more seats are expected to be declared afterward.

Earlier today, speaking to his supporter at the party's headquarters, he described the election result is the "sweetest victory of all."