David Cameron: EU reform is 'not an impossible task'
The prime minister will set out his aims in a letter to European Council President Donald Tusk, paving the way for detailed talks among EU leaders.
He has committed to negotiating a "better deal" with the EU ahead of an in/out referendum by the end of 2017.
Campaigners for Britain to leave the EU say the renegotiations are a gimmick.
Meanwhile, Europe minister David Lidington has said the government hopes to get a deal agreed as early as December, when a key summit of EU leaders takes place - but he cautioned that it was too early to guarantee exact timings.
'A big task'
Mr Cameron has said he wants the UK to stay in a reformed EU, but he has not ruled out leaving if he cannot secure the change he wants.
His letter to Mr Tusk will be the first time he has set out in writing the details of what he wants to achieve.
In a speech ahead of its publication, he will say four objectives lie at the heart of the UK's renegotiations:
§ protection of the single market for Britain and other non-euro countries
§ boosting competitiveness
§ exempting Britain from "ever-closer union" and bolstering national parliaments
§ restricting EU migrants' access to in-work benefits
Around 40% of EU migrants who have arrived in the UK over the last four years are supported by the benefits system, new analysis from the Department for Work and Pensions suggests. Of these, around 66% receive in-work benefits.
Source: BBC News
