In reply to oldie:
Did a route off beach at Langdon a couple of years back and the way down was at least at that time, fine. You have to descend a steep ladder after the tunnel right at the end. From there, you move under The Tube and Great White Fright areas east to St Margaret's. It's a long walk even along the cliff top from Langdon to St Margaret's, but there's a nice pub at StM for refreshments
It sounds like a brilliant adventure you have in mind. I had one of my hottest, most hilarious, most scary and most eye opening days ever, climbing on those cliffs and I would go back there in a heartbeat - it is just brilliant. Genuinely think it's one of Britain's best bits of coastline. The people are amazing too, from the locals in the pub, to the police we met on the beach who were 1st point of contact for migrants, whose boats we saw being towed in pretty much all day. What a crazy day we experienced. I hope yours is just as interesting. Go steady and let us know how you get on!