I'm desperately after some recommendations for good nurseries in any of the above areas. My baby is 8months old, I have recently started him at Barnet Hospital creche where I work but I'm not sure how I feel about it. The price is similar to all surrounding private nurseries and I think that they will have much better facilities.
Not in the area you mentioned but worth a look is Cedar Park (Wolverton) in Enfield. It is right next to Chase Farm (which I believe is linked to Barnet Hospital, so there must be some kind of transport between the two).
My son went there aged 18 months until he went to school last September. I felt really confident that he was in good hands. Lots of cuddles for the babies, lots of activities for the older ones.
It is a beautiful old house with huge grounds. They even have their own wood where they go on Gruffalo hunts. They do lots of interesting outings and activities.
The only downside is that the hours are a bit limted. And woe betide if you are late..
Can heartily recommend Head Start on Station Road in New Barnet. DD has been there since she was 11 months old (she is now 4). She loves it there. They have a wonderful outdoor area. It has a great atmosphere when you walk in too.