Britain has ratified Croatia's accession treaty to the European Union, paving the way for Croatia to join the union after six years of tough negotiations.

British Foreign Office said Britain on Monday deposited documents of ratification with the Italian government, the depositary authority for the Treaty of Rome, in advance of Croatian President Ivo Josipovic's visit to Britain later this week.

The ratification paves the way for Croatia to accede to the EU on 1 July 2013, once remaining EU member states have also deposited their documents.

"The final step was taken this morning by our Ambassador in Rome who deposited the Instrument of Ratification with the Italian government. The UK now looks forward to welcoming Croatia as the 28th EU Member State on 1 July 2013," British Foreign Secretary William Hague said.

"The UK Government is confident that Croatia will be ready in full and I welcome the commitment that Croatian government ministers have made to ensuring that the reform momentum continues post-accession so that the benefits can be harnessed in full," Hague said.

Josipovic will meet with British Queen Elizabeth II, Prime Minister David Cameron, Business Secretary Vince Cable and Justice Secretary Chris Grayling during his visit in Britain between May 22 and 24, the Foreign Office said.