Stealing this!
Whilst the UK hasn't got a hope in hells chance of some form of retaliation against Russia, there are a lot of Russian Oligarchs in London with a lot of property. Would be easy to put travel bans on them and seize this property until they could prove how it was funded (which probably half of them won't be able to do).
Any other sort of response will just get laughed at.
It was my understanding that all of the people associated with the Russian ruling elite are barred from visiting the EU and other western countries as per Ukraine related sanctions. There is nobody left to bar from visiting the UK. If you add Magnitsky act then it covers pretty much any and all people (unless I mis-remembered).
The other wealthy Russian are the ones who fell out of favour with the current elite in Russia so there would be no point in punishing them.
What is left to do? I do wonder what is a reasonable response to this.
I think expelling the Russian ambassador and placing sanctions on people who they think are involved (probably already under sanctions) is the most the UK can do.