I have done a quick search of proof of funds thread links as I have a couple of questions around proof of funds.

I am intending to take bank statements or a cheque for the required amount and the house valuation obtained in spring last year. I have just under the required amount by $500 due to the fluctuation in the pound in liquid funds, so I guess my question is will my mortgage valuation be enough given that I am selling my house.

Last minute panic!!

Valuation is not valid for proof of funds upon landing. All funds must be liquid or easily transferable. Those tied up in property do not count.

Can't you borrow a few hundred quid from someone temporarily?

You can't use equity in your house when you land, the funds must be unencumbered at that point. It's ok to use equity when you first apply (London is the only visa office that allows this), but you will need to show the actual cash when landing to activate PR.

Does that help? Good luck.