Loss of power at low revs and noisy engine?

My car has just started being quite sluggish at low revs, like not all the power is going through, and the engine sounds quite bad. Its like I can hear the cylinders, like a bad sounding slow turning V8 (if that makes sense?). Its not overheating. Its also the first time I've really driven it in the cold, although it was in rush hour so the engine warmed up quite quickly and the problem continued. Any ideas what could be wrong? Meant to be going away with it the next few weekends but feeling a bit anxious about it now!

Sounds like it may not be running on all cylinders, which will result in loss of power and irregular running/engine sound. To confim you could remove the HT leads from the spark plugs one at a time with engine running (hold the lead with something to insulate it so you don't get a shock). You will notice a change in the engine rhythm each time you remove a lead, if you don't than that cylinder isn't firing. Then it's a case of fuel or ignition.

Cheers