especially the many enemies of Putin who have settled there
I don't think that many of the Russian oligarchs are enemies of Putin. They wouldn't be commuting on a regular basis between Russia and the EU if they were (see the extract below)
A significant number of Russian oligarchs have bought homes in upmarket sections of London in the United Kingdom, which has been dubbed "Moscow on Thames."
[30] Some, like Leonard Blavatnik, Eugene Shvidler, Alexander Knaster, Konstantin Kagalovsky and Abram Reznikov, are expatriates, having taken permanent residency in London. This community has led to journalists calling the city "Londongrad". Most own homes in both countries as well as property and have acquired controlling interests in major European companies. They commute on a regular basis between the EU and Russia; in many cases their families reside in London, with their children attending school there. In 2007 Abram Reznikov bought one of Spain's mega recycling companies, Alamak Espana Trade SL, while Roman Abramovich bought the English football club, Chelsea F.C., in 2003, and has spent record amounts on players' salaries.[31]
en.wikipedia.org/wiki/Russian_oligarch
The whole article is interesting.
I have no problem with Russians making their home in the UK. I have no problem with any people from any country making their home in the UK.