The Brits have withdrawn the €500 note from circulation in the UK, on evidence that the vast majority of them are used by those conducting illegal business:
However, fed up with abuse of the currency, Britain's Serious and Organised Crime Agency (Soca) has decided with the Treasury and Home Office to remove €500 notes from circulation in Britain. Soca's ban follows an investigation which revealed that 90 per cent of the €500 notes in this country are being used for criminal purposes. It's the latest of a number of high-denomination bank notes favoured by villains that have fallen out of favour. Richard Nixon halted the circulation of $10,000 bills in 1969 because of their association with organised crime; these days the 1,000 Swiss franc note, while rare, is another popular choice for those engaging in nefarious deeds, and the 1,000 Dutch guilder note was a black-market favourite before the introduction of the euro.
It's not exactly clear to me how they're doing this, since the euro isn't a British currency to begin with – are they forbidding banks from accepting them in transactions?