Depending how far you want to go there are quite few LFS in greater manchester.
As im not into marine, wont comment marine sections of shops below
Pets at home in Stockport - very nice choice of plants including tropica, but personaly dont feel comfortable buing anything else there, especialy fish
Pets at home in Trafford - Smaller than stockport one.
Abyss aquatics - not far from pets at home in stockport. Very nice choice of fish, but i wouldnt expect too many oddbals or rare species. Usualy nice choice of angelfish, L-number plecs. last time ive been there there was nice choice of different apisto's. Extensive range of tank on display. They also stock JBL food and gear which is quite rare for uk.
Oasis - walking distance from city centre, bit cramped but nice choice of fish and gear. Reasonable staff giving good advices (rare thing). Plant wise - not to big choice unfortunately.
Urmston aquatics - good gear prices, not too big choice of fish unfortunately. Plants also only typical common species). They have RO water on sale.
Gordon Riggs Rochdale(garden centre) - Atm growing back their pets department after last year fire, fish and plant wise choice is not great, but they have one of biggest choices of difrent types wood for hardscaping tanks ive seen in greater manchester including large pieces and its reasonably priced.
BAS (bolton aquatics superstore) - largest LFS in area, massive fish range. They stock few far east brands of equipment and tanks - great prices but you have to be carefull about quality in some cases.
If you are willing to travel bit further there are few Maidenhead Stores reasonably close to Manchester. They are especialy good if you need bit more choice in plants and related gear.