Poor security is the main cause of bike theft.
Always lock your bike – the frame and at least one wheel – to something secure to avoid it getting damaged and reduce the risk of it being stolen. You may also want to remove lights and pumps.
Aim to spend around 10% of the value of the bike on a lock, the best ones are approved by Sold Secure. Most cable type locks are not as secure as shackle types, but a length of cable is useful to secure wheels and other components.