UK Citizens do not need a visa for stays of up to 90 days in Kosovo, however you will be required to disclose the reason for your visit. If you intend to visit Serbia, you will be unable to do so without transiting through a third country's border to receive an entry stamp. Serbia do not recognise Kosovan permit stamps and can refuse entry if you have these in your passport.
Your passport should be valid for the duration of your intended stay.
The information found here is based on the response provided by the embassy. We recommend you always double check the latest information directly with the embassy before you travel. If you wish to travel for longer than the visa-free period, you should speak to the embassy directly on 0207 405 1010.