Tina wrote:

The tomatoes are really small, only the size of a 1p piece, and very
dark in colour. The flavour is superb.Â* Anyone have a clue what variety
they might be?

From the description, possibly these?

https://www.thompson-morgan.com/p/tomato-cherry-black-opal/tm54731TM

That doesn't say that they're F1 hybrids, but if they are and you grow
from their seeds, the offspring might vary wildly from the parents ...