Sorry for the late reply.
Common sense would say I replaced the HT leads, but I didnt.
Anyway I bit the bullet and purchased new coil pack, new HT leads and new spark plugs last week (as euro car parts had a sales on ) as this has cured the misfire
However.....
I still have the problem that started all this. I can be driving along and the speedo will drop to zero for a few seconds (although I can still accelerate) and if the radio is on it will go quieter, then it will suddenly kick back in. Everybody I have spoken to says a new coil pack would have sorted this, but it hasnt....any ideas?

Thanks again for the help so far, I really appreciate it