Code for Rover 218 sld radio?

When having work done on my Rover 218 sld recently, the garage disconnected the car battery. Now the radio doesn't work (the anti-theft lock having been activated when the battery was disconnected). I have got the seriel number from the back of the radio, but need the code to re-set it. I have found lists on the internet, but they all seem to cost about £20 before you can see the code for your car's specific model. Any suggestions on a cheaper (preferrably free) method of finding the correct code? thanks, Bill