How many Spitfire Mk ll and Mk1 and Mk1a were in use in the Battle of Britain ?

Does anyone have rough figures of the quantity of Mk ll spits in use during the BoB period compared to Mk1 and 1a, not after a precise figure, just some idea will do !
To have a breakdown of figures per month even better though not expecting such miracles.
There are a few dome noses in use at Dunkirk, but I see mostly pointed spinners in BoB photos, though one flight sim features mostly domed in stills I see from it. I prefer the look of the de Havilland Spinner personally.

What were the differences between a Mk1 and Mk1a by the way, any external differences ? I recall something to do with engine but would like to know.

DBenz