Armed Robbery UK

Note:I am not a lawyer.

In Britain it depends on his age, but if he's an adult 5 years is the statutory minimum for a fire arms offense (The Fire Arms Order 2007 but there are earlier provisions with the same effect).

Other things affecting sentencing and which category of prison he was sent to: whether he really had a gun or it was fake, other offences committed in the pursuit of the crime, the impact on the victims and how much he stole. Also his motive would be taken into account, as would past history.

If his actual robbery carried a lower sentence tarriff he still may go down for 5 years for the seperate count of carrying a fire arm.

Here are the CPS guidelines: http://www.cps.gov.uk/legal/s_to_u/sentencing_manual/robbery/

http://www.hmcourts-service.gov.uk/

You'll probably find lots of useful information there. Worth spending a few hours combing through it so you can get things like procedure correct. (or watch some episodes of Law and Order UK, it should be available for download somewhere)