I don't use a Brooks brand saddle. But I use sprung ones on all of my bikes. My old English 3 speed has a unknown leather one. My Dahon Boardwalk has a stock one with the "Dahon" logo stamped clearly on the back end. And my Brompton got one recently that is a Nirve:

www.nirve.com/parts.asp?cid=3004

for it's touch of retro California beach cruiser appeal in a Lounge Lizard pattern!