If you don’t want to fanny around with opening an account and risk the price dropping while the shares are deposited… the registrar (will most likely be either computershare, equiniti or capita), will probably offer online sharedealing for UK certificated holdings. Just make sure it’s an actual certicate you have and not a statement of holdings. Don’t forget to send them the certificate when they ask for it. No certificate=no money (and an expensive buy back)
Also make sure the certificate is valid before you trade (call the registrar, number will be in the back of the certificate)
I work in the industry and have seen a lot of cert deals go tits up.
Iirc cash settlement is still 10 working days after trading for cert trades