But of course they can only offer these prices because the wholesale prices for roaming are capped across the EU (this has been the case for a while now, they h

But of course they can only offer these prices because the wholesale prices for roaming are capped across the EU (this has been the case for a while now, they have now just reduced those rates further). If the UK operators wouldn't be able to benefit from the wholesale prices anymore, I doubt they could sustain this. Just look at Switzerland, where "all in" contracts with roaming in the EU will set you back around 70-90 CHF...