David Cameron is facing the fraught final stages of negotiations to secure a new deal for Britain's relationship with the European Union as he prepares for a crunch summit in Brussels.
The Prime Minister has been warned he has an "extra mile" to go to persuade eastern European leaders to agree to proposed reforms and is also battling to keep his party together as Eurosceptic ministers get ready to speak out.
Senior figures in the European Parliament also continued to warn that MEPs may reject key elements of any package signed off by leaders later this week
Ska Keller, vice-chairwoman of the Greens and European Free Alliance group, said it was "very important" the final agreement does not include discriminatory measures and echoed warnings by the chamber's president, Martin Schulz, that the plans would not be nodded through.
She told BBC Two's Newsnight: "If parliaments were only there to nod things through then we could as well get rid of parliaments but we don't want that, we want to strengthen democracy in the European Union.
"There's been a lot of criticism about the European Union not being democratic enough. I think those people shouldn't criticise us for actually exercising our democratic role.
"We are directly elected by the European Union citizens. I think citizens of the European Union and also Great Britain will expect from us that we have a very close look as this."
Conservative mayoral candidate Zac Goldsmith again insisted he will only announce his voting intentions once the Prime Minister has secured a deal but reiterated his Euroscepticism and insisted Britain had a "bright future" whatever the outcome.
Downing Street conceded there "are still details to be nailed down" to secure an agreement this week but insisted that Mr Cameron's talks with key figures in Brussels on Tuesday had been "useful".
The Prime Minister was told he has an "extra mile" to go to persuade the Czech Republic, Hungary, Poland and Slovakia to back the deal. The group has made it clear it opposes significant welfare reforms but No 10 is keen to avoid watering down the package.
Britain's renegotiation is the first item on the agenda for the European Council summit on Thursday, but the gathering of 28 EU leaders is not scheduled to conclude until Friday lunchtime, after which Mr Cameron will call an immediate Cabinet meeting if he secures a deal.
The meeting will effectively fire the starting gun on the referendum battle, as Eurosceptic ministers will be given the green light to campaign for a Leave vote in the poll expected on June 23.