Let say you have Canon 40D, 50D or similar. For sport low lighting my recommendation Canon 70-200 F2.8 IS ( Image Stabilization).

It depends on how close you can get to the action and what shots are important. The best lenses are fixed focal length with wide maximum apertures. If you have to use a variable aperture zoom, the wider the zoom, the wider the aperture which means the faster the shutter speed you can use to stop action.

Minimum shutter speed to stop action is 1/250 and faster is better. Depending on the high ISO capabilities of the camera you're using, you may be limited by the amount of noise.

Action shots are best if the peak movement can be anticipated. That and understanding the sport to know what classic images to look for.

I assume that because you're in the UK, you're referring to shooting soccer (when you say football) so I'll leave you with an image of Pel