Justice Secretary Michael Gove told Tory activists that there has to be a 'genuine people's movement' fighting for EU reform to avoid a superficial deal

Ministers must not ‘fudge’ EU reform, Michael Gove has warned – as Poland threatened to block David Cameron’s plans for immigration and welfare changes.

In a pointed intervention, the Justice Secretary dismissed suggestions that Britain could only hope to achieve a superficial deal.

Speaking to Tory activists in Hampshire, he said: ‘It’s an opportunity that history will not forgive us for fudging or failing to grasp.

'Let’s make sure that the arguments aren’t left to the Prime Minister and to ministers in government, but that a genuine people’s movement stands behind that fight for change.

‘And let’s make sure that we are optimistic about what we can achieve, because if we allow ourselves to be constrained by the judgments of the commentators, then we will falter and we will fail.’

His comments came as Polish prime minister Ewa Kopacz warned that she would not accept any proposals that ‘discriminate’ against her countrymen working in Britain.

Mr Cameron wants to ban migrants from claiming benefits for four years, and bar them from sending child benefit home to children living abroad.

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David Cameron held a press conference on Friday in Riga. He wants to ban migrants from claiming benefits for four years as part of a number of reforms that have raised concerns among other European leaders

But Miss Kopacz, who will hold talks with Mr Cameron on Friday, said she would not accept changes that did not also apply to British citizens.

At a press conference yesterday, she warned Mr Cameron that he ‘cannot make any moves which would discriminate against Poles’.

The Prime Minister will depart this evening on a whirlwind tour of European capitals to drum up support for his renegotiation strategy. He will travel to Denmark tonight for talks with prime minister Helle Thorning-Schmidt in the morning.

He will then fly to the Netherlands to meet Dutch PM Mark Rutte, before heading to Paris for talks over dinner with French president Francois Hollande.

On Friday he will meet Miss Kopacz in Warsaw, before finishing the 3,000-mile trip in Berlin for talks with German Chancellor Angela Merkel.

The charm offensive took an early blow on Monday when it emerged that Mrs Merkel and Mr Hollande have agreed a deal to shore up the euro by tightening political union between the Eurozone countries without the need for treaty change.

Polish prime minister Ewa Kopacz (left) has warned Cameron against any moves that would discriminate against Poles. Cameron will meet her on Friday before sitting with German chancellor Angela Merkel (right)

The move is a potential blow to Mr Cameron, who believes treaty change will be needed to enact his key demands. But No10 played down the move, saying the Prime Minister remained confident he could achieve the changes necessary.

SNP leader Nicola Sturgeon yesterday stepped up her demands for Scotland to be given a veto over any move to leave the EU. She said: ‘We will propose a double majority, meaning that exit from the EU would only be possible if all four nations of the UK agree, something that would ensure Scotland couldn’t be forced out of the Union against our will.’