Homebase won't stock specialised nutrients like that, you'd have to go growell.co.uk or do a search of hydrophonics stores either online or on location. Growell is the most commercial hydrophonics branch that I have seen personally, they are the only people with actual walk in shops and not just a depo, they're also the cheapest I've seen. They got one store in London and a few in the bronx (urban areas out of london), if your worried about ordering shit like that online, don't, its a legal business and a legal product