Ignition coil problems, after replacement

I have a 2003 Fabia 1.4, which was fine up until a couple of weeks ago. It started losing power for a second, and the EPC and Engine light would flash on but then immediately go off.

The day after it did it more often, and started struggling to pull away. It was also not going about 2000 rpm, even with my foot flat to the floor. A few revs would get it going again though. The RAC had a look, and it showed misfire on one ignition coil. As it was a pack they would all need replacing, but I couldn't get the part on a Sunday, and I was away for the weekend.

When I set off home the day after, it wouldn't pull at all, so the RAC came out again and said now all 4 were misfiring. I got recovered, and on the Monday got the part and fitted it. Everything seemed fine, with the occasional splutter.

A couple of weeks later, the spluttering has got more common, and tonight it was struggling to pull at all, and cut out completely a couple of times when I pressed the clutch to change gear. When I got home (it cut out as I came up to my drive), it took 3 or 4 goes to actually start, but revved fine once it did start.

Could this be something wrong with the new coil pack that I fitted, or is it more likely to be something else on the engine causing it?

Anyone else had similar issues with replacing coil packs?

Thanks.