There's a difference between SWAT or border patrol and regular cops on the street. They still have SWAT teams in the UK, they just acknowledge that the times you need to go in guns-blazing are the exception to the rule.
The UK doesn't really have SWAT. Ordinary people are most likely to see firearm officers with an MP5SF or similar, a black semi-automatic carbine, which a typical civilian probably mentally files as a "machine gun like in a movie" and its main purpose is to act as a visible deterrent and set them apart from "ordinary" unarmed police officers.
Many officers armed with the expectation they might need to actually shoot somebody, not just act as a deterrent have Glocks, because a pistol is the right tool for this job, and they may have also been trained to use a military-style shotgun. But that's about as far as it goes.
If the bad guys have a rocket launcher, in the UK the expectation is that this is now a problem for the Army, not some nutjob with a badge who thinks Judge Dredd is a role model rather than a satire.
Many officers armed with the expectation they might need to actually shoot somebody, not just act as a deterrent have Glocks, because a pistol is the right tool for this job, and they may have also been trained to use a military-style shotgun. But that's about as far as it goes.
If the bad guys have a rocket launcher, in the UK the expectation is that this is now a problem for the Army, not some nutjob with a badge who thinks Judge Dredd is a role model rather than a satire.