There are two type of property that may be taken from you when you are arrested
1. The property in your pockets etc. when arrested (e.g. coins, watch, lighter, wallet)
Any property which is not believed to be of evidential value (and is not an illegal item or substance). This should be returned when you leave custody.
2. Property you own which is of interest to the investigation (e.g. a computer, a large sum of cash, trainers or kitchen knives).
The policy may differ from force to force but generally you should receive some form of notification, probably in writing, stating that you can collect your property and where to go for it.
Do not just turn up at the police station if you have not had previous notification from the officer in the case, as it is unlikely that you will be able to collect the property. The property cannot be returned to you until the officer in the case has authorised it for release.
The police can keep relevant property until a case has been resolved and in some cases they can keep it after conviction (in case of a hearing relating to the confiscation of any illegal assets, or a possible appeal in some circumstances).
If you want to make some enquiries as to whether you can collect your property, you need to speak to the officer in the case.
If you have been notified to collect your property and fail to do so then after a certain amount of time (will vary from force to force) the property will be disposed of (either destroyed or sold at auction).