I wee bit further south than the rest but ho hum
Aquator (Hele Road, Hele, Torquay, Devon)
Very good, has a large marine section as well as the usual tropical and coldwater - as well as reptiles and hedgehogs
Something Fishy (Queen Street, Newton Abbot)
Another very good LFS - not so much marine - but a lot of freshwater
Maidenhead Aquatics @ Jacks patch (Teignmouth)
Recently revamped and I believe more of this to come - no marines at this bracnch but coldwater and tropical specialists - always a good selection of fish etc here
Pets at ho... - uuumm on the other hand

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