Hi. I was able to get some boxes (free) from "Bookseller Crow On The Hill" very close to the Crystal Palace junction, on Westow Street, SE26 3AF, 020 87718831 (For exact location, Streetmap.co.uk is good if you enter the postcode). Ask in advance if they have some, how many you want and arrange collection time (so to avoid customer disruption). Parking is iffy. The boxes are strong, so ought to stack well if packed with integrity, they are clean and of equal size, but they're not big since books weigh heavy and there's a limit on what one is expected to carry if full. From memory something like 12" high, 20" length and 18" wide.
Could also try Kirkdale Bookshop, more or less opposite what was The Greyhound, but I haven't asked there.
You could try somewhere like Curry's etc if you need bigger boxes (e.g. Downham trading estate? near the bus station - I forget the name).
Good luck with the move
