The only Instant bacteria I trust is Bio-spira, that should be kept in a fridge. I have imported some from america via cold pack and airmail, it still works as it should. With this, you do need to add all fish at once along with Prime and then the cycle is pretty instant. With this product you should not use any ammo-lock as it can hinder the bacterial development. I would recommend this to anyone, it really does do what it says on the packet.
http/fishstoretn.com/bio_spira.html
Is the store that ships to UK, cost me 24.99 dollars so about 16 pounds.
EDIT I did it because I actually wanted to see for myself if it really works, I am curious like that!!