I do not know if these are sold in the UK or not. Less lumens.
https://www.planetbike.com/superflas...ke-tail-light/

That light has very wide coverage, not just straight directly behind you.

For touring, I have two taillights on my bike. A regular Superflash and the Superflash 65. For straight roads, I use the plain Superflash that has a very narrow focused beam. For hilly or winding roads where the traffic is often not directly behind me I use the Superflash 65.

Foggy or overcast conditions, I use both.

Both take two AAA.