Remember when teh Irish decided to back depositors in their banks with 100% guarantee of all of their money, and when Germany decided to ban naked short selling. There were the usual howls and squeals and condemnations saying that they should have waited for Godot and multilateral agreement. The Irish were desperate and had to take that action to maintain confidence in their banking system, but others told them to wait for Godot. If they had waited, they would have been sunk. The Irish did the right thing.
Why did it concern the howlers and squealers what the Irish did? What were they scared of? They were frightened that if Ireland unilaterally guaranteed deposits, then there might be a run on UK banks, and people might take their money out of UK banks and put it in Ireland. That is why they were desperate to prevent Ireland acting unilaterally.
The Swiss are strong enough to act unilaterally and so are the US. Neither of these countries are stupid. They don't want to wait for Godot, they want to act unilaterally now, in order to restore confidence in their banking system. I think the reason that Mandelson warned them against doing so, is because he would then have to do something similar in the UK in order to maintain confidence in our system. So why doesn't he do that and follow what the Swiss and the US are doing? The reason is because he can't. The Robert Peston article showed that the UK banks would not be able to easily raise the capital that the Swiss were able to raise. So he wants everybody to wait and act together unilaterally, so as not to expose any country which is not capable of acting. But the other countries are not prepared to sacrifice their countries for the sake of those who are not able to act, due to their weaker financial system. They will do what the Irish did, and act in their own national interest, and not in the national interest of other countries. Note that it was teh strong countries, the USA, Germany and the Swiss who wanted to act unilaterally.