I have a very good essay about that.
Have to scrape it together and type, bit busy at the moment.
From memory the LW lost with almost complete verification some 1200 aircraft (elevenhundredandsomething) aircraft to RAF guns in a given period, which BTW does not cover the whole, if you go June to November, the stats AFAIK get worse for the LW.
100 are credited to ack and the rest to various other incidents, totalling some 1700.
Operations are all BoB related.
I belive I have posted those already, just can't remember where

Anyway, the RAF losses are quite near the 900, and honestly, that high figure from Izzy is more or less impossible, - not enough planes to fill the figure.
Deightons book is actually quite good, and his book "Blood tears and Folly" is a worthy read, IMHO much better. Fighter is also good, but it has some bugs in it, and the one that triggered me was his turn calculation (109, Hurry, Spit) which is completely a contradiction to the laws of physics.
So, it's a worthy read, but take it with a grain of salt. Since Deighton easily broadcasts gibberish like that, I re-read his books from a little distance.