Trimar aquaria based in Camborne Cornwall offer a mail order tropical fish service.  You can buy tropical fish online from them with the added security of knowing that the fish will arrive next day safe and sound.  I purchased two large clown Loach from them about three years ago and they are still nice and healthy and my tank.  They will ship anywhere in the UK with a next day delivery guaranteed.

   Trimar Aquaria Purchase Tropical Fish Online