The chairs of the main political groups in the European parliament have told David Cameron they will deal with any legislation necessary for his reforms "swiftly".
The trio - who represent 481 of the legislature's 749 MEPs - told Mr Cameron they supported his proposals for changes to the bloc.
A No 10 spokesman said: "All three made clear their support for the proposals on the table and said they were ready to take any necessary EU legislation through the European Parliament swiftly."
If a deal is reached, the Prime Minister is expected to hold a referendum on Britain's membership of the EU in June.
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His meeting with the three senior MEPs came after the head of the European Parliament Martin Schulz said he could not guarantee the legislature would back Britain's EU reform deal.
Mr Schultz said the European parliament would deal with any legislation necessary as a result of the changes after the referendum takes place.
But he added: "To be quite clear, no government can go to the parliament and say: this is our proposal, can you give a guarantee about the result. This is not possible in a democracy."
But Downing Street stressed any pact reached at a crunch summit of EU leaders this week would be a "legally binding document under international law", and so the European parliament should support it.
Mr Cameron also met European Commission president Jean-Claude Juncker who, No 10 said, "agreed that the talks on the UK renegotiation had progressed well" before the pair discussed "issues where there are still details to be nailed down in order to pave the way for an agreement".
When asked earlier, Mr Juncker refused to consider the prospect of a so-called Brexit, insisting there was no "plan B" as he expected the UK to remain as "a constructive and active member".
Mr Farage said: "The real truth is that this deal is not worth the paper it's written on. It is subject to European Parliamentary approval and ultimately judgements of the European Court of Justice."
Mr Cameron has agreed to hold an emergency Cabinet meeting on Friday if he secures an EU deal at the Brussels summit.
The meeting will see the suspension of "collective responsibility", so members of the Cabinet will be free to express their views and support either the "leave" or "remain" campaigns.