The lanes are round the Hailsham area - you can see them with maps here -
http://www.wanderlustonline.com/firle - if you do the marked runs take care with the last one, it is TIGHT and VERY soggy !
Firle is a nice scenic run with a slippy twist in the tale just before Alfriston, however it is perfectly doable with road tyres.
Folkington is a lovely tight lane best done from the Folkington end where you go up a tightish hill coccooned by the trees.
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There's also a pretty little lane close to the Fox & Hounds in Fox Hill :)
Before doing any I would suggest you contact the ROW office on 01273 482354.
Trev