Secure your bicycle with a good quality solid lock. If your wheels have a quick release system, remove the front wheel and secure it to the frame and back wheel. If other parts are removable, take them with you. Park your bike where passing pedestrians can see it.
If possible, insure your bike, have your frame postcoded and make a note of the colour, frame size, make, model and any other special details. This information will help the Police if your bicycle is stolen.
There are cycle lockers in the Chapel Street and Assembly Rooms car parks which are free of charge. Cyclists need their own locks to secure them.