British Standards show the minimum criteria that a product should meet in order to do its job well. Locks come as British Standard, showing that they are high enough quality and strong enough to do their job and withstand a certain amount of force.
With something as important as a door lock, it is very reassuring to know it meets British Standards. It is something that will be protecting your home, and it should be as high quality as possible. You can research the brands that meet with British Standards to check you are getting quality locks.
If you are using a locksmith, it will indicate a certain amount of quality if they install British Standard locks. This shows they care about their customers and will only use quality materials, putting you are ease about the service they provide. Do your own research as well, to make sure you are getting the right locks.