Hi. I haven't lived in the UK for years. An when I did I couldn't bring my snakes, but friends had some. ASF can be found if you Google. From what I remember some Brits made a stink about feeding live.

Live here if your local shop doesn't carry them:
african soft furred rat - Rodents, Rehome Buy and Sell | Preloved

Frozen prey:
Frozen Foods – Rattlesnacks

All the best!