I don't believe your mortgage company has to allow a port, it's completely up to them. They can say no, it can be a new property they don't want to lend against. People regularly move in / out with partners and want to sell. There are hundreds of reasons why circumstances change and having a fixed mortgage can make it harder to deal with and negotiate through.
Your right, not all lenders allow porting but that's one of the questions you ask upfront before signing up to a fix. Likewise you are correct that you would have to meet their lending criteria but in reality most mainstream lenders are petty much the same these days for normal every day applicants. If you've suddenly gone self employed in the last year or two, then good luck getting any lending anyway.
"Interest rates can only go up" has been a catchphrase for 10 years now, in which time they've gone much lower than they are now and not gone up anywhere near the speed or percentage points people have expected. What I can guarantee will happen is people fix for 5-10 years and "100%" say they don't plan on moving, changing circumstances etc.... and then in 3 years scrabble about trying to work out how to pay £10k to get out of the deal as they are getting divorced, moving in with a partner, having a career change and moving away etc....
Most lenders allow the porting of mortgages and its very unlikely that they will not lend on the onward purchase unless you A) cant afford it or B) its a very unusual property, in which case you'll be SOL with all mainstream lenders anyway. I don't make financial decisions here and now on the basis that I might get divorced in the future, if your thinking you might get a divorce, its probably not a good idea to fix your mortgage and perhaps the money may be better spent lining up a family solicitor.
A £10K ERC would mean you have pretty healthy mortgage balance, an ERC is normally 1% per year and most peoples balances are just not that high unless they literally just bought the place and live in the south.
But genuinely interest rates cannot really go any lower. From what I understand the last year was basically the lowest you can get. As in banks wouldn't lend at a lower rate.
Exactly, people may have been saying it for years and it did actually start creeping up in 2018/19 before COVID hit. During COVID the rate was 0.1, it really couldn't get any lower for consumers in the retail space. Now we have massive inflation and there is a fairly clear direction of travel as has been indicated by the Bank of England to try and get it under control, that is to raise rates to soak up some of that QE they were pumping into the economy. The question is by how much and how quickly, it might be slow, it might not, that's the roll of the dice you take when deciding to fix or not.
I'm not saying you should fix or not and lots of people have done well by not fixing in a falling economy (as many did with energy prices in the early stage of the pandemic). That situation could change in the near future, it might not, I don't know but neither do you.