accelerater

Hi, I have a Seat Ibiza 1.2 petrol. Its 3 years old and was serviced and MOT'ed about 2 weeks ago, just as i bought it. Its been working great, but last night i changed from 4th gear to 3rd, and the accelerator did nothing, no revs at all. so put it back in 4th and away it went. i got home...