There's less gas in countries who normally bought from Russia, therefore there's bigger demand for gas from other sellers. They reach to sources that UK used to buy gas from. When there's so many countries willing to buy and less sellers, those who are left, are putting prices up.
Regarding cap, I wish I knew too... I bet politicians in the UK don't want to put cap like other countries and charge more in taxes later on, but that's my guess. Obviously countries that have cap on energy prices now, are going to charge for it in higher taxes later on or less funding for other things like healthcare, roads, schools. On the other hand, aren't they wasting taxpayers money already? 😖