Not actually Bletchley, but my youngest went to Little Bears nursery in Simpson (about 3 miles from Bletchley) and it was fantastic. Much better than the other various nurseries we used. Small and really caring place, with a great garden and really experienced and lovely staff. The only trouble is that because they are small they don't have many spaces, so you might need to get your name down now for June. They have a website if you google them.