Apart from Dartmoor, wild camping in England & Wales puts you in a dubious position unless you ask permission. Generally it's tolerated if high up, away from farmland, done sensitively, unobtrusively and on open access land.
I never wild camped in Kent, but I used to live there and I could suggest some places. Probably bad form to do so publicly. Why don't you have a look at the livefortheoutdoors forum? My username is the same on there and it has a PM system.
As said by sanhozay, unless you get the landowners permission it isn't permitted. Try somewhere that is actually wild like north Northumberland, Scottish highlands or Dartmoor. Just don't stray onto any military ranges.
As far as I know the English laws are fairly restrictive on Wild camping. i.e you can't do it except in Dartmoor. Scotland and some of Wales are more accepting. I have found a site in Ashbourne that offers a wild camping experience. It's not close to you but may be an option.
The ukcamping link is: Rivendale
I'd be interested to know if you have any success
------------- Bananas are a good source of potassium
Just visited Forge Wood - brand new site and likely to be closed now but perfect for what you want. Good opportunities to hone your wildcamping skills (see all the reviews.)
------------- 2011-
Dec/Jan -Cornwall nr Padstow (cottage)
Feb - our garden (tent)
March - Llangollen (cottage)
March -Town Farm, Bucks.
April - garden..again..need to get out more...
May - Acoustic Festival of Britain Uttoxeter
Glad to be of service - I thought it was amazing, some people there had literally set up camp with all branches and twigs making up sink units, tripods for campfires etc - perfect for what you need I think.
------------- 2011-
Dec/Jan -Cornwall nr Padstow (cottage)
Feb - our garden (tent)
March - Llangollen (cottage)
March -Town Farm, Bucks.
April - garden..again..need to get out more...
May - Acoustic Festival of Britain Uttoxeter
you can wild camp pretty much anywhere on council land ,they have little powers to stop you or take so long to act your long gone .try the warren near folkestone! crapping in the woods is very common