Not sure about Norway, but in the case of UK and Ireland most police officers are not allowed anywhere near firearms.
If an incident takes place that requires armed officers a senior policeman authorises the use of armed unit. Every force has access to them, and training is as much about de-escalation and negotiation as shooting. They are drawn from regular police and undergo significant extra regular training.
Wikipedia tells me roughly 6,000 of something like 140,000 UK police are authorised to carry firearms.