How can I check the securiy code for my radio?

I had a new battery fitted and ever since the radio does not work and is requesting a code. I have tried several times to put the code in, but it still does not work. I bought the car second hand. Could anyone check to see if the code I have is incorrect as the garage want to charge me £25 to tell me the code which maybe the one that I already have. The code I have is 1229 and the serial number is BP026318397143. If you need to know its a Rover 45. Thank you.