This lock isn't available with a key override. The Lockey 2200 is the only product currently available with a surface lock. All of the other mechanical digital door locks with key override have a mortice latch.

I would recommend the Codelocks CL290 - Back to Back which has a code plate on both sides. This type of lock requires a code on either side of the door to open it.

This lock can be used for an outside gate in his manner.

Changing the code can not be done quickly but is relatively easy to do. Please see the Lockey 2200 Surface Lock User Guide to see the exact process. This lock is suitable for any external application providing that it is fitted to a door which is 35-55mm thick.

Unfortunately, none of the mechanical door locks comply with British Standards. You would need to use an insurance approved deadlock in order to meet the standard.