Now im not an electrician but i have done all my own and know a thing or 2 (i hope!) Now to start of with are you sure they are mains wires because anything in the attick is usually lighting wires unless you live in a coach house! if they are lighting wires then do NOT attempt to use those!! In answer to your question (if they are mains wires!) then yes you can use them and there shouldnt be a problem at all. To determine properly you need to find out what circuit you are planning on tapping into and what the rating is on the breaker in the fuse box. Then you need to find out exactly what other sockets are on the circuit and add up all the appliances on them to find out how much power is going through the breaker! the breaker in the fuse box should always have around 4 amps spare so its not fully loaded.............for example..... if you add up all your appliances (using amps = watts / volts) and you have say 10 amps in total on your circuit and your breaker is 20 amps then you could add around an extra 5 amps to that circuit safley! If i was you i would run 2 double sockets up there from a mains point and have the 2 lights on a 10amp control box (this will use up one of the double sockets) then put the heater on one plug socket of the other double and a trip out extension lead on the other for the pump and fans and whatever else! I actually have what i just described up in mine, i will try get some photos to show u if u want! Hope some of this helps or makes sense. Any questions then ask and i will try 2 help!