Speedometer trouble

Hi, I am having a little trouble with my BMW 316i,
All of a sudden the speedometer has become eratic, it sometimes works and sometimes doesn't it just sit there while the car is moving, and seems to work whenever it feels like it, does anybody know what the problem is? Its an H reg so its quite old, but has done just over 60,000 miles

Any help will be greatfully recieved.

could be you SI card behind the dash going out