David Cameron today suffered his worst day yet in his bid to reform the European Union as his plans were rejected by four countries.

The Prime Minister met with leaders in Brussels as part of a charm offensive to try and renegotiate the terms of Britain's membership of the EU ahead of the referendum.

But the intensive round of diplomacy turned into a humiliating series of set-backs as each of the four leaders he held one-on-one meetings with rebuffed his proposals.

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Belgian Prime Minister Charles Michel made clear to David Cameron that his proposal for a four-year ban on migrants claiming benefits was a 'non-starter'

Belgium said his plan for a four-year ban on migrants claiming in-work benefits was a ‘non-starter’.

The move to curb the welfare bill, which Mr Cameron has said is an 'absolute requirement' to keep Britain in, was also rejected by Romanian president Klaus Werner Iohannis.

In further bad news, after holding meetings with Mr Cameron the Finnish prime minister Juha Sipila and Spanish prime minister Mariano Rajoy both said they would not consider changing EU treaties despite him saying this is essential.

Downing Street has privately been hoping a renegotiation of Britain's membership of the EU could be completed as early as Christmas, paving the way for a possible in-out referendum in the spring of 2016.

But Mr Cameron needs to get agreement on his proposals from all of the other 27 EU states, meaning he could be faced with major embarrassment if they dig their heels in.

In the latest round of his charm offensive, Mr Cameron held four bilateral meetings at the EU-CELAC meeting of European, Latin American and Caribbean nations at the European Council in Brussels today.

At a breakfast meeting, the Belgian prime minister Charles Michel told Mr Cameron that the renegotiation ‘will not be easy’.

His spokesman later said that the proposed changes to curb in-work benefits for non-British workers in the hope that removing the state subsidy for low-paid work will cut migration was a ‘non-starter’,

He added: ‘The equality of European citizens for us is a crucial point of view.’

Finnish prime minister Juha Sipila ruled out the idea of changing EU treaties, which experts say would be needed to secure the changes Mr Cameron wants

Romanian president Klaus Werner Iohannis told Mr Cameron that he would not support attempts to curb benefits for migrants in the UK

The Romanian president came out of his meeting with Mr Cameron and told reporters he would resist the move too.

Asked if he would want Romanians citizens going to the UK treated differently from British citizens in terms of entitlement to social benefits, he said: ‘Well, obviously not, because it's my best interest to have Romanians treated as European citizens everywhere in the European Union.

‘No member state is allowed to treat people coming from elsewhere different from its own people.’

No member state is allowed to treat people coming from elsewhere different from its own people Romania's Klaus Werner Iohannis

However, Mr Cameron is understood to have taken comfort after Mr Iohannis said migrants moving to claim benefits without any intention of getting a job was a ‘major problem’.

Mr Cameron insists that full treaty change is needed to secure the reforms he wants to the European Union, but he also faced opposition on that.

Juha Sipila, the prime Minister of Finland told Mr Cameron he is not ‘eager’ to enter a ‘carousel’ of treaty negotiations.

His spokesman added that said he hopes another method can be found to change EU rules without rewriting its underpinning legal texts as that would open a ‘Pandora's box’ that will result in a flood of demands from other countries.

Spanish diplomats said that Mr Rajoy told the Prime Minister that Spain is also against treaty change, telling him ‘It can’t be done’.

Spanish prime minister Mariano Rajoy said he would not consider changing EU treaties as part of Britain's call for reform

A Downing Street spokesman last night admitted that Mr Cameron still had a long way to go in persuading other EU member states.

She said: ‘The Prime Minister set out the issues he wants to address as part of this EU negotiation and clearly there are going to be more discussions needed.

‘We’ve expected that. We have said that this process is going to take time and patience. There will be different views expressed along the way, but what matters is the Prime Minister is determined to address the concerns of the British people and to work with others to find solutions to them.’

There will be different views expressed along the way, but what matters is the Prime Minister is determined to address the concerns of the British people Downing Street

Asked if the talks had not gone as well as hoped, she added: ‘Tere some countries that are more likeminded and others less so.

‘So I think we have had and continue to have realistic expectations of the different views around the table and the work we will have to do to persuade people.

‘There is a clear sense that people recognise there are issues that the British people want to be addressed, there will be a choice for the British people is that in or out, and ahead of that referendum we need to work together with EU partners to look at how you can address those concerns.’

A fortnight ago, Poland rejected his benefit plans as a ‘definite no’, but Angela Merkel provided a major boost as she declared that 'where there's a will there's a way' about the prospects of compromise.

Mr Cameron wants to speak to every EU leader before a summit in Brussels later this month where there will be a discussion of the UK’s concerns.