British taxpayers could face a bill of up to £43bn to bail out the European single currency through the IMF after a Brussels 'stitch up'.
Chancellor Alistair Darling was left powerless as EU finance chiefs led by France and Germany cobbled together a plan that will leave Britain liable for the debts of failed economies that are tied to the euro.
Details of the deal were initially thrashed out at a meeting of EU leaders on Saturday in which Britain played no part. Last night at a meeting of EU finance ministers, the Chancellor was due to sign up to plans for the European Commission to give 'balance of payments' loans worth £52bn to failing economies.
This would leave the UK saddled with a £5.2bn bill if they default.
That fund already offers tens of billions of euros to non-eurozone countries but will now be widened so all 27 EU countries can grab the funds - making the total British liability £9.5bn.
Ministers from the 16 eurozone countries have already approved a £95billion bail-out for Greece. But economists estimate that if Portugal, Ireland and Spain eventually require similar three-year bail-outs, the total cost would add up to £430bn.
Britain pays 10% of the Commission's bill and if the loan fund had to take the strain, Britain's share of the liability would be £43bn.
EU finance ministers were rushing to do a deal last night before the financial markets opened overnight in Asia.
The Chancellor denied that Britain was involved in propping up the euro after he signalled that he would block a second initiative to create an EU-wide version of the International Monetary Fund. The idea being advocated by France and Germany would give government-backed loan guarantees to the euro's failing economies, leaving taxpayers liable for all their debts.
As he arrived in Brussels, Mr Darling made clear that the UK would not sanction such a move - which required unanimous support - but said the eurozone countries could take that step on their own if they wanted.
He said Britain would 'play our part' in helping to 'stabilise the situation', but added: 'When it comes to supporting the euro, obviously that is for the eurozone countries.'
But he was effectively forced to support the separate balance of payments loan fund after other EU leaders made clear that under the Lisbon Treaty Mr Darling was powerless to stop it being passed.
Fears of a 'stitch up' were fuelled after President Nicolas Sarkozy's office released a statement saying France and Germany had agreed measures to deal with the financial crisis.
Critics warned that EU leaders were taking advantage of the confusion over the status of the UK government. Mats Persson, director of Open Europe, a Brussels reform think tank, said: 'What we're were told would never happen has now occurred.
'British taxpayers have become directly liable for the mess created by the failed euro experiment. While it's in everyone's interest for Europe's economy to stabilise, this deal could easily spiral out of control.'
Treasury officials stressed that the fund Britain is signed up for will not involve putting in any money up front. The UK would only be landed with a multi-billion pound bill if there were defaults.