Are you a member of the AA /RAC? If so, use them in the first instance. If not I assume that this has happened as you have parked up and applied the handbrake. This could be that the cable mechanism has seized somewhere between the actual handbrake lever and the where the cable splits to each brake (it would not normally be that the actual brakes have seized). You could try just holding the handbrake lever (with the button held in), pull it up to its fullest extent and slam it down hard a number of times. Failing that, try putting the car in reverse and sharply let the clutch out (to the point of stalling) a number of times.

If none of that works then it would require the car to be jacked up (securely,not by using the standard vehicle jack) so that you can access the underneath. If you then follow the handbrake cable you should see a point where it splits at 90 degrees to each wheel, where you could release the cable so that it frees the brakes. The most likely fault is lack of lubricant at the connection points on the handbrake cable. Let me know how you get on.