The Crime Survey for England and Wales (CSEW) has collected data about bike theft since it was introduced in 1981. It’s a relatively small offence, accounting for approximately 5% of all crime covered by the survey, and the number of reported bike thefts has declined since 2012.
However, that doesn’t mean you can forget about security. Many thieves are opportunists, and are more likely to take a bike if it’s easy to do so without getting caught. The cost of bikes has increased, too, giving people more incentive to try and sell them on. The more secure your bike, the less likely it is to be stolen.