cold apartment - draft behind plasterboard wall

I moved into a 2nd floor apartment just before Christmas (there's the one floor above us). We only got around to putting the wall lights in the kitchen/living room last night. The builders left the cables sticking out of the plasterboard wall with and they were covered by 2 grey plastic boxes.

Anyway, a mate of mine who's a sparks was putting the lights up and found that there was a draft coming out of the holes in the plasterboard.

Presumably, this cold wind blowing around behind the plasterboard is the reason why the apartment was impossible to heat during the winter just gone?

Can someone confirm my suspicions that this is indeed a bad sign? Even better, if someone knows what I could do about it could they please let me know? If I approach the builders I know I'm very likely to be brushed off unless I have something to say that will force a bit of action from them. Does homebond cover this sort of thing?

Any advice or info would be greatly appreciated

The building regulations -or better the technical guidance of them- stipulate a draftfree building. So get these, copy the relevant page and present it to the builder/seller when making your claim. Check the previous posts to get the adress of "Oasis" (or try google), the gouvernmental info web site.There you'll find the "technical guidance documents".