In reply to laurentb:
Hi Laurentb.
There's some chalk over just north of Luton and a bit over near the A5 cutting near Dustable.
There's some minging chalk walls above the Meads between Ware and Hertford tt I used to see from my train to work, but they were (are) behind warehouses.
There are a few chalk quarries scattered around the A10 north to Cambridge too and of course there is (was?) Cherry Hinton (Cambridge).
Cherry Hinton is the only one of these I've ever climbed in - I wouldn't want to climb somewhere worse!
Good luck!