Passiflora variety, with a fruit, maybe?

Nope. Creeping Fig (Ficus repens), in its adult form. Once it turns purple, the fig will be edible, but not very tasty.

Interesting Tug, not one I know, or at least, I've never seen ...

Most of the UK is out of its comfort zone, though from your account of London weather lately, that may be changing. I would be cautious in planting it though--it's worse than ivy where it's happy, and it has eaten a few old homes around here.

Tug, re weather here - its been really cold the last couple of days, frosts at night again, hail, sleet and some rain today (welcome rain here anyway). Which likely means this Ficus still wouldn't be happy here I'm guessing...

It can take some light frosts--it is the hardiest of the evergreen Ficus species, but prolonged cold and sleet, etc. probably would do it in.