I’ll be reassessing what I am paying towards HIS house - given I am paying essentially more than half (as currrntly I’ve seen no evidence that the bills have increased) he is indeed the one in a much better situation with me living there
This lack of financial transparency rings an alarm bell for me, @Dogmummy1980. Ime, when one partner in a relationship is cagey about money matters, it's usually because they are hiding something.
Why are you paying more than half the outgoings? I can see that it could be argued that more energy and water is used by you and your children than he would use if living alone, but that doesn't apply to all outgoings.
He would have been entitled to a 25% discount on the council tax while living there alone, so that has only gone up by 25% (mycounciltax.org.uk will give you the exact figure). Insurance will be very little different. Maintenance will also be little different.
I also think it is inequitable to pay half the mortgage. You shouldn't be paying anything off the capital amount, and if he's had the mortgage for several years, that could be a big chunk of the monthly repayments. And you definitely shouldn't be paying half of any home improvements that will ultimately benefit his children.
Ime, secrecy about money is usually because someone has something to hide. I think if you have agreed to pay half the running costs of a home, you're entitled to know exactly what they are.
I think it's time for a very frank conversation about how things are arranged between the two of you. I think your concerns about your security, and that of your children, should he predecease you, are entirely reasonable. That would be my starting point. It wouldn't be unreasonable to look at both your pension arrangements, too. If one of you dies, would the surviving partner be entitled to something from your pensions, for example?
If you can reduce what you are paying him towards the costs of running the home, that would mean you can clear your debts more quickly and save the deposit on a BTL property sooner. Then at least you'll know that you and your children have somewhere to live should the worst happen.