British Prime Minister David Cameron | EPA/Andy Rain David Cameron cancels meeting with European Parliament leaders British prime minister will now lobby the assembly’s main political groups separately.

David Cameron canceled an eagerly awaited debate with European Parliament leaders on the U.K.'s renegotiation of its EU membership scheduled for Tuesday, citing "time constraints."

The British prime minister was expected to make his case for EU reforms at a meeting of the Parliament's political group leaders just two days before a crucial EU summit where leaders hope to agree on his proposals for U.K. membership in the Union. Instead Cameron will meet separately Tuesday in Brussels with leaders of the European Parliament's major parties, as well as with its president, Martin Schulz.

Schulz had been pushing since September for Cameron to explain his proposals for avoiding a Brexit to a full session of the Parliament. But Cameron had agreed only to discuss his reforms at a closed-door meeting of the Conference of Presidents.

That group is made up of leaders of the assembly’s political groups, including such controversial MEPs as Nigel Farage, head of the strongly Euroskeptic United Kingdom Independence Party, and Marine Le Pen, head of the far-right National Front.

"The Prime Minister has turned chicken," Farage said in a statement. "He knows that not only is his deal pitiful but that in an open Conference of Presidents I would be able to expose the fact that even if he wins the referendum, the Parliament will veto its terms."

“I sincerely doubt that group leaders will provide guarantees to Cameron that they will not veto on migrant benefits,” said a Parliament official. “We can’t give any guarantees on something we haven’t seen yet.”

"Cameron may have wanted to avoid Farage,” the official said.

A spokesperson for Schulz said: “We haven’t discussed guarantees, tomorrow we will discuss the concerns of the European Parliament concerning the proposals.”

"The Parliament decides by a free vote of its members not by a decree of the president.”

A spokesperson for the European Conservatives and Reformists group, home to Tory MEPs, said group leader Syed Kamall had a meeting with Cameron last week.

"There's a possibility of a meeting tomorrow but we're not pushing for it as there are other uses for his (Cameron's) time," the ECR spokesperson said.

Last week the ECR was calling for a political agreement in the Parliament on controversial elements of the reform package, such as cuts to benefits, ahead of the referendum.

“We’d like a vote before the referendum,” the ECR said Monday.

Liberal MEP Sylvie Goulard said Cameron's decision was "an affront to democracy."

David #Cameron refuse de venir au Parlement européen ? Déni de démocratie.

https://t.co/rB3IFYxSVe #UKinEU — Sylvie Goulard (@GoulardSylvie) February 15, 2016

The reform proposals, laid out in a 16-page text, are the result of months of negotiation and shuttle diplomacy. They aim to make the EU more palatable to British voters before a referendum on whether to stay in the Union is held later this year. They include reforms in four major areas: competitiveness, eurozone governance, national sovereignty and welfare benefits for EU migrants.

The European Parliament has had no role in drafting the proposed U.K. deal but the assembly will get the chance to debate and vote on Cameron’s most contentious proposal, on welfare benefits.

At a recent technical session of diplomatic advisers to EU leaders on the proposals, the Parliament was represented by its secretary-general, Klaus Welle, Schulz’s cabinet chief, Markus Winkler, and three leading MEPs — Elmar Brok, Roberto Gualtieri and Guy Verhofstadt. That same group will also meet with Cameron on Tuesday morning, according to Parliament officials.

Parts of the draft U.K. membership deal require the Commission to submit new legislation to the Parliament, while other parts can be decided with the unanimous approval of all 28 EU leaders.

MEPs want a bigger say on other parts of the draft proposal, including items that would undermine what little power they have, such as the proposed “red card” mechanism which would allow national parliaments to veto EU legislation.