You won't get anything that seems at all authentic.
Larger branches of Tesco are open tomorrow and, if they're anything like the big one on the edge of Ipswich, they will be awash with cream ('cos I bought some there just before they closed yesterday, expecting them to have run out, and they'd got loads left).
Some are, some aren't. Tesco Extra stores are generally open but some normal Tesco stores aren't. Asda are open (but the Ipswich one had totally run out of all types of cream yesterday afternoon and they might not get a delivery before you'd want it). Most Morrison's stores are open, as are Sainsbury's.
I think I read somewhere, melting 4 fl oz milk with 4 oz butter (taking care not to boil it) then whisking will produce cream. I haven't tried it yet though, just kept info incase I need it in the future. I've actually whipped evaporated milk with a bit of icing sugar and vanilla essence for a topping for jelly. Or you could make a 'mock cream' by making a white sauce and adding icing sugar, vanilla essence and butter then whip when cool.