It's better they take the guns off the security guards as they are obviously not a deterrant
Is it true that the common police in the UK do not carry fire arms? If the police in the UK have no fire-arms, it is not so far fetched to say that the local armaguard vans should not carry weapons.
Its a tough situation, if they have guns the criminals just use bigger better guns, and if the security guard actually shoots then they are tried as a murder suspect like that woman who was beaten up.
It really comes down to trying to calculate if them carrying guns deters more crimes occuring, or if the fact that they carry guns is an incentive for the criminals, as quite often the guns are part of the looty.