I don't Gobions Wood, but know Ashridge fairly well. I haven't been to Potters Crouch plantation for a couple of year, but recall that it was great for fungi - though I'm not a 'fungi person'.
Whippendell Wood in Watford is notable for having the only record in Britain of Crepidotus cinnabarinus, which is also only the fourth European record:
Whippendell Wood :: Watford Borough Council
If you want to know more about Whippendell Wood it's only 20mins walk from me, so I can advise you where to park etc..
Jim