As it is YOUR hobby, you can do it YOUR way. If you keep a personal lifelist or countrylist, you can tick what you want adhering to your own criteria. So, if you want to tick escapees or exotics, it's up to you in my opinion.
However, if you find it important to compare your tick numbers with others than you should adhere to the standards of the same authority. For Britain this should be the BOU, but on a worldwide scale you should use a worldwide authority like e.g. the Clements list. And of course you can make a combination list: you keep your personal list as it is, and you add or delete the lumps and splits when you want to make a comparison via an authority list.
And when tick numbers are very important to you, then move to the Netherlands as Michael Frankis suggested. But this highlights immediately the problems in comparing tick numbers, the Dutch Committee has more splits recognized than the British, and I think that also the American AOU will be different again. Adhering to these "official regulations" makes that you have no say in your PERSONAL list. But there are already enough authorities prescribing what you have to do with your life, it is nice to escape from them now and then in YOUR hobbies.
When you are visiting e.g. the Netherlands or France, are you then keeping to the BOU list, or are you then adhering to the local official list? Another dilemma.
For MY own list, when I see a bird in the wild, not being in a zoo or a collection, able to fly, and no people chasing it to get it back into its cage, then I tick it.
So I recently added the Rosy-faced Lovebird / Agapornis roseicollis to my PERSONAL list, when I saw two of them happily feeding and flying around on the coast in Dunbar, Scotland. Of course, they were not in my guide, but I made a good drawing and found them back in HBW. Horror to some people, I know, but it is MY list!
By the way, are House Sparrows and Starlings not tickable in the USA as they have been brought there by man not too long ago?
Regards,
Peter
P.S. Thanks for the blessing, CJW B