Many thanks for the reply.
Probably should have mentioned that I've already changed the spark plugs and the coil pack. Ive read a lot about faulty coil packs so cant help thinking it might be that....is there any way to check a coil pack??
My focus doesnt have a MAF sensor, at least not one I can find, when I googled it, it said some 1.4's & 1.6's had MAP sensor instead of MAF sensors.
Its not missing at idle or when revving, just under load.
Seems there are quite a few things it could be then

Thanks again for your reply