How many individual types of aircraft have served in the RAF since its formation in 1918?

I’m asking this question as I’m an instructor with my local ATC unit and would like to know for an aircraft recognition class I’ll be teaching next year. By individual aircraft I mean all major variants, Harrier GR1, GR3, GR5, GR7 and GR9 would count as 5 different aircraft. Tornado 3, F2/3, GR1, GR4 but aircraft such as Spitfires and Hurricanes are much more difficult as continuously uprated during war.

Thank you in advance if anybody has either counted themselves or for directions to a relevant website.

Probably incomplete but:
http://en.wikipedia.org/wiki/List_of_aircraft_of_the_RAF

Harriers (for example) were also updated as many GR3 were converted GR1 airframes while others were new build and particularly in recent decades this has been the case as airframes become ever more expensive.