Ford Fiesta '05 Revving On, Very Noisy Acceleration Problem?

[RHG]

After changing gear and slightly pressing on the accelerator pedal my car makes a loud excessive revving noise, the accelerometer ticks over yet my car doesn't speed up excessively and when i'm setting off in first makes me sound like I have my foot flat on the accelerator pedal. It is a problem in second and third gear too. If I put my foot any heavier on the pedal it doesn't affect the speed of my car just lets out a loud revving noise, makes it very difficult to drive, is anyone aware of what could be causing this problem? Thanks