"The RAF did not prevent many raids reaching and bombing their targets"
Ditto for 99 percent of all large raids in WW2. Preventing bombers from ever reaching the target was not a reasonable expectation. There were a few exceptions, and most of those are well covered. Even the Schweinfurt raids in 1943 with no fighter escort, flying into an area well covered by 1st rate radar of the day got through. Air War is a war of attrition, in almost all cases, from 1916-2009.
Re any cannon armed RAF fighter in the BoB: No. 19 Squadron for a few weeks did use the Spitfire IB as Shifty said, it had 2 x 20mm hispanos. It represented probably less than 1 percent of the total sorties flown by RAF Fighter Command. They had too many problems with jamming and were withdrawn, although the initial results were promising enough that the cannon idea was still worked on. There were no cannon armed Hurricanes at all in the battle, not even a single one. Just in case there are any lingering doubts. There were a few squadrons of Hurricane IIAs and IIBs, but these were definately not in any large #. Those were armed with 303s. There were a few Spitfire IIAs, also armed with 303s.
Just on a historical note regarding the pilots in the RAF at the time. The RAF could not have held out without the large # of aircrews from the British Commonwealth; Canada, Australia, New Zealand, S. Africa, Rhodesia, ect, and the foreign nationals; the Free Poles, Free Czecks, Free French, and some from the USA, some 487 "foreign pilots" in total. The transfers from other commands such as Bomber Command, Coastal Command, the Fleet Air Arm and Training units also were vital. They got anybody that could fly a fighter. It was a rather interesting bag of nationalities and individuals. Rather than the 1930s RAF which had been described as "the worlds most exclusive flying club" it more resembled a flying circus in the BoB, with many pilots from different parts of the globe. Of course the majority were English, Scot, and Welsh, and Northen Irish, from the British Isles.
