Poland's main concern centres around a specific part of the voting system which allows countries to delay an EU decision if they fall just short of the required number of countries to block it.

Warsaw claims it secured a gentleman's agreement at a meeting of EU leaders last month, allowing countries to delay decisions by up to two years.

However, the written mandate for negotiating a new EU treaty only promises a reasonable delay, which some officials say should not exceed four months.

According to Mr Kaczynski, it was "a technical error" not to explicitly type in a two-year blocking period to the final agreement.

"We negotiated two years there and it does not appear [in the text] because – let's be clear about this – nobody signed anything there. Everything was verbal. It all took place very fast and in the early hours of the morning, after two days of talks", the reportedly tougher of the Kaczynski twins said.

The EU voting system – introducing a double-majority principle, based on the number of countries and their population size – was the main stumbling block of the contentious negotiations at the June summit. Warsaw claimed the mechanism is designed to favour the biggest EU players, while it weakens the power of medium-size states like Poland.

In the end, after threats of launching treaty talks without Polish approval, EU leaders finally reached unanimous agreement – after Warsaw managed to delay the new voting system from coming into place until 2014.

But Portugal – currently sitting at the EU's helm – has repeatedly dismissed Poland's attempts to reopen this key part of a hard-fought agreement, saying the mandate was clear and precise.

UK's Brown under mounting pressure

Meanwhile, UK prime minister Gordon Brown has come under strong pressure from the unions to call a referendum on the resulting treaty, which they say has maintained the essence of the original EU constitution.

"Europe can only be developed with the wholehearted support of its citizens", Paul Kenny from the GMB general union said according to the Daily Telegraph. He also urged the Labour Party to stick to its election promise to hold a popular vote.

"The pledge was right at the time of the general election and it is right now", he said.

The GMB pools 590,000 members and is close to Mr Brown's Labour Party – something that plays against Mr Brown and places him under pressure from both the left and right.

The unions have attacked the fact that London has secured a special exemption from the Charter of Fundamental Rights - a document listing the citizens' civil, social and economic rights declared binding in the EU's new treaty blueprint.

"A Reform Treaty on the constitution without the Charter of Fundamental Rights is for a business Europe and the GMB did not sign up for this", Mr Kenny said.