Come on, now. Criminals don't have guns in London.
For its size, London has virtually no shootings at all. It had over four times fewer murders than New York City, and NYC is regarded as rather safe by US standards.
The shootout scene was well-done, but as a plot point, it's simply not something that would happen in LONDON, of all places. Maybe a stabby fight with some knives and one or two people literally getting gutted would have been more realistic.
But even then, you're talking about a city with only 100 or so murders all YEAR, and no single incident is going to account for more than 5% of the total or so. So it would have to be limited in scope.