i was driving around near haywards heath, west sussex . and all of a sudden this noise developed and gradually got worse as i drove home (aprox 5 miles) i topped up with oil thinking it was low, and it calmed it down a little, but its still making that noise? there is also a bit of oil under neath the car, but not sure if it was there before this problem.

I filmed it to explain it better

http://www.youtube.com/watch?v=o1Dzwm_noUw

everything under the bonnet is standard for this 1.4l fiesta (the backbox is making the rumble)

its also lost its top speed and lost ALOT of acceleration

any help would be appreciated

That doesnt sound very well at all. Could the exhaust be blowing? It would explain the loss of speed and acceleration. But then so would any major engine problem. I'd definitely get it looked at sooner rather than later mate. Get it on a ramp and you might be able to see the problem straight away.

sounds like a sticking valve or two.

Judging by the sound of it (not the best of quality so cant be too sure) band the fact that when you topped up the oil it "calmed down" would think your bottom ends away. You might get away with fitting new shells.

Would bottom end going get that bad so quickly though?

Can do if it was seriously low on oil and the engine was quite hot. Could be a big end bearing.