President of the European Council Donald Tusk has confirmed receipt of a letter from Prime Minister David Cameron outlining the terms of treaty change he wants to achieve.
Tusk said on Twitter: "Acknowledgement of receipt. With David Cameron's letter, negotiations on UK in EU can now begin".
The EU Commission has also said it is now ready to work for a fair deal for Britain, that is also fair for all other member states.
The letter is the formal document of the treaty change demands, which Cameron outlined earlier when he spoke at Chatham House.
Tusk has now said negotiations can begin, with other European Union leaders having previously said that discussions on treaty change could not begin as they did not know what Cameron actually wanted.
The letter outlines proposals for reform being in the areas of economic governance, competitiveness, sovereignty and immigration. Cameron wrote:
I hope that this letter can provide a clear basis for reaching an agreement that would, of course, need to be legally-biding and irreversible – and where necessary have force in Treaties
I look forward to a substantive discussion at the December European Council. It remains my aim to conclude an agreement at the earliest opportunity, but the priority is to get the substance right.
While Cameron has been trying to convince other European leaders of the need for treaty change for some time, "substantive" negotiations had not started as there was not a formal request of what the the Prime Minister wanted to achieve.
Cameron also said during his speech today that the outcome of the promised referendum will be "the final decision".