Thanks all. My dad actually died (fsck cancer) a couple of years ago now, but it has taken this long to sort out his house.
I’ve checked on overpayment and can do 10% without charge and it will have an impact on interest (I can essentially choose to keep the payments the same and shorten the term, or keep the term the same and reduce the payments). It struck me that this might be handy if interest rates go up.
My thought was that, if I did move for work in a year, maybe keep the house as rented out for year until I get settled, then sell it. That would give me about two years of having the money work for me. Premium bonds have been less than stellar as a return for me so far. Maybe I should resurrect my old ISA.