OK well looks like it was the 3 blue botias. Went to my normal shop this morning and he refuses to stock them for the very reason they can get very nasty at night time, they are nocturnal and appear very placid during the day. However you look them up on the web and one site will tell you they are community fish and another site will tell you they are highly aggressive fish I know what my 3 fell under! Oh and one hadn't been killed, it was just hiding next to the plec, not being eaten by the plec as my parents thought

So called up the shop I got them from today and not only did they allow me to choose other fish to the value of the 3 blue botias (£12) but also another tenners worth to replace the fish that had been killed which I thought was more than generous bearing in mind they weren't legally obliged to do anything as I had no proof of anything.

So they have stuck the 3 killers in their display tank (which is huge) with some very big fish so as they will learn their lesson if they try anything nasty again

What I got can't replace the specimen fish but at least the tank should calm down now and it well stocked again with some nice fish

Thanks for all the replies. Just hope I got it right in picking out the blue botias as the culprits (they were the last to be introduced and all dead fish have occured since their introduction). Also when I explained its all mid weater fish that have been killed that made perfect sense as they sit on the bottom at night and sleep and thats when the 3 blue botias will have attacked them, not during the day when they were all swimming about.