I've just drilled a hole through the wall(or least I thought I had) anyway
the hole was where there already but needed to widen it to accomadate
passing a BB cable through.

Started on one side but was met with resistance so I decided to drill
through from the otherside,again met with resistance but eventually got
through only to find there was one and a half holes on the otherside of the
wall.

Looks like someone had attempted to drill the wall(probably with a short
drill bit) and was guessing the distance with an iffy tape measure. ;-)