Orpster,
Just read your post, I had been on holiday so sorry for the delay in replying.
If the diagnostic light is showing then it is almost certainly an ignition coil. Mine was the 150bhp which does not have coil packs and this is where my confusion came from.
As yours is a 170bhp then it has a single coil pack per cylinder and it is a fairly cheap part.
Check out some of the posts on here for coil packs, you'll soon find what you need.
Cheers.