"while the UK refuses to choose between the EU or the US and those hundreds of millions of european customers with a single currency."

The Brits shouldn't be in a position of choosing between EU & US as far as Trade- they should be able to have both- ever hear of this thing called Free Trade? Perhaps if there are a lot of people in EU which think the Brit must choose between trading with EU or US, then the UK should reconsider joining the EU, and other members might be wise to reconsider their memberships.
Though I doubt that any sizable number of Brits see joining the EU as cutting off economic relationship with the US.
As far as switching to the Euro, the Brits want to do this at a time when it's favorable in terms of their national interests, but generally speaking switching to the Euro should be in the UK's national interest, but it's a matter adjusting their economy, and ensuring that this change will not cause harm to their economy due the inability of the government having the power to make any needed adjustments. So there are internal changes being enacted in Britian, and also I believe there is some clarifications they are seeking in regards to the existing and possible future EU laws & procedures.
If when the Brits switches currency, the Brits are prosperous as a result, this would good for the EU, if instead it suffers economically then that would be worse for the EU. If the UK misses the opportunity to switch as soon as they are ready, then they will, of course, lose out on some of the possible gain they would have otherwise realized.