I'll agree it sounds immoral on the face of it but we need an answer to this crap for the greater good because it's only going to get worse otherwise.
If the latest fatal shooting, this time of a small child, don't float your boat for toying with the idea of bit of extra-judicial you must have someting other than blood in your veins.
Police harrassment of the Evil 15, the known but 'above the law' gunmen is a good start but let's get creative. Let's get the SAS involved: they don't take prisoners.
Here's how it works.
For a specified period reverse the presumption that those who get arrested get bail unless the police agree waive that on a case by case basis.
Continue to harrass the ass of the gunslinger's minions until they are nailed for something, like intefering with an officer in the course of his duties, littering or breathing in and out in a threatening manner.
While they are in jail pending a bail hearing the SAS who have been spirited into the country draw numbers to decide which gunslingers get an unexpected visit. Some entrepreneur could even run a little numbers racket on the side here. Pick 4 from 15.
Nobody ever sees anything anway so they won't see the bad guys being snatched even if it's done in broad daylight accompanied by a marching band - but of course it will be a lot sneakier than that.
If that doesn't quite things down repeat until it does.
Naturally the Police aren't involved in any of this extra judicial stuff, just uphold the law and make the initial arrests for minor offences. And of course it would be their duty to investigate these disappearances to the usual high standards with the usual level of witness co-operation and support from the public.
Get it done while the UK politicos and media are caught up in General Election fever and too busy to poke around investigating a few missing criminals, who may have fled the island anyway because things were getting too hot. How did they leave? Who knows, same way the guns get in probably.
Deniabilty is built right into the whole process. The criminals 'advantages' are all turned against them. Poetic Justice.
Sorry Gordon but enough is enough - those who dare win.