KamKam

You must remember that to shoot or trap any animal or bird in your own garden legally,that specific animal/bird must come under the conditions of the General Licence as set out by (Natural England) previously done by (DEFRA).
A copy of which can be viewed on the BASC site or other similar body.
If a compalaint is made by a neighbour then the police may pay you a visit.They can prosecute for any criminal/firearms offences such as firing outside the boundary of your garden or criminal damage but it will be an RSPCA inspector who can and may prosecute for any wildlife offences.

Be warned and beware that if you draw attention to yourself and you are a Shotgun or Firearms Licence holder then that can and may be revoked pending any investigation!

In my opion, unless you live in the countryside with no close neighbours,leave well alone and let nature take its course with the magpies.
I should know I am one of the above and shoot myself on a regular basis,but to start shooting wildlife in your own garden in this day and age with lots of anti's about is not worth it!!!

Good luck
Combat Cook....