Anyone know what effects pedal this might be?

[gingataff]

How about a Catalinbread? They make a few boosters although I'm not sure how easy they are to get in the UK. Their Super Chili Picoso has 35dB of clean boost.

[Twinfan]

How about the Keeley Katana boost. Indysmith has/had one I think.

Does this mean you're selling your RC booster then?

The Katana boost sounds interesting, I'll check it out.

I won't be selling the RC booster, no.  I always hang on to pedals I've bought in case I ever need them in the future  :)

Thanks for the other booster suggestions too guys, I'll take a look at them all...