@Neil, cost, awkwardness of getting to the pipe, I'm told it uses old fittings which can no longer get, plus the fact that the drips aren't too frequent (yet!).
I saw a youtube video of this compression tape and it looked ideal for the job.
It's a leak on a joint. I'll try to get photo up over the next couple of days.
I hear what you're saying re replacing rather than covering (I think replacing the pipe will be a pig of a job for whoever does it) - I need a quick fix as the room in question is getting plastered next week.