I have a friend who used to run a pistol club (pre Dunblane).
When you use the phrase "highly trained firearms officers" he usally goes very pale and then laughs. He can tell you stories about these guys that you would not belive.
As for the highly trained Met firearms squad - there is the story about the firearms officer who was shooting at a club and put 2 rounds through the table, 2 into the ceiling baffle and the fiftth down range (into someone elses target) - the entire met team had their shooting privilidges withdrawn by the club secretary and were asked to leave the club.