Just to update my own question:
stayed at Lee Valley for 8 nights last week, and it was very good. Excellent location for North London and access from M25.
It was obvious most people on site at this time were working, but the site is well managed and vans/trucks are offsite with no early morning revving! Even the hardy fools in tents seemed civilised.
Shower blocks are spotless, warm and loads of hot water. Wardens are very helpful, and seem to keep a close eye on things. Secure 10pm-8am.
The site is next to big multi-screen cinema, golf course and canal walks. Unfortunately the adjacent pizza restaurant has closed so there is nowhere to eat except snacks in cinema. Two pubs within 20mins walk, but didn't fancy the walk at this time of year.
Big Tesco, IKEA, 10 mins drive.