Whilst the OP might be poorly written and researched, it has prompted quite a reaction on here and that's what it's all about.
I've been back in the UK for a year after 18 years in Thailand so am probably in a better position than most to comment.
The obvious expense differences are in property, either rent or purchase, eating out, fuel and utilities. Groceries are probably a little more expensive but my partner, who's here at the moment, believes that most meat is no more expensive here that in Thailand. I'm not talking Waitrose of high street butcher prices, of course, but lower end supermarkets. Even bananas are the same price here. If you eat a predominantly Western diet, grocery shopping in the UK is probably cheaper than Thailand but add a few more exotic ingredients and the tables soon turn.
I bought a secondhand car for 70,000 baht. 10 years old. The GF expected an unserviceable old banger but she was surprised to see a decent runaround that would cost around 250,000 baht in Thailand..
I think people's circumstances should be taken into account. Not everyone is living off a UK state pension, renting a cheap bungalow and living off noodles and phad khaprow. If you are then don't even think about returning to the UK.
Unfortunately I am one of those idiots that sold my house. I'd be totally self-sufficient had I not done so, however the proceeds funded my lifestyle in Thailand, including a business the GF now runs. But it was a huge financial mistake.
I have a private pension, no state pension yet, and savings but I am also a professional in my field and have been able to pick up lucrative contract work whilst still calling myself semi-retired. This has enabled me to pay a high rent in West London. I have no school fees to pay and no medical insurance costs (though I have kept a basic policy with a very high excess on the go in Thailand as I probably will return sometime and don't want to end up unable to buy insurance).
NB the OP's comment about being unable to register with the NHS is simply untrue. All you need as a National Insurance number and proof of citizenship.
My daughter works part-time in a restaurant and attends a school (free). She funds her own clothes and expenditure and even gets child benefit.
There are aspects of Thai life I miss but I'm enjoying pubs, English beer, gigs, theatre, the arts, country walks, and free public transport (being over 60 in London).
Yes, I'd spend less in Thailand but money is not the be all and the end all for everybody. I'll be back sometime, when I no longer want to work (or nobody wants me!) and when my daughter finishes her education.