Hi 24041303
There is also Elstree (website here>>
Home) and there is a microlight site at Graveley, just north of Stevenage. The one to the west of Stevenage is probably Rush Green but I think that is just a maintenance operation (i.e. no training).
A bit further afield you have Cambridge, Cranfield, Denham, Stapleford and North Weald.
A good aviation map can be found here
SkyDemon Light. It's actually much more than just a map but it shows most airfields and almost certainly all the airfields with a PPL flight school.
Enjoy the PPL
Raiz