I'm a long time B17 user. I bought a bike from Spa in Harrogate and got it with the default saddle, a
Passport Navigator (reviewed
here). The Spa guy said they were the cheapest decent saddle they could find and that most people ordered a different one, or fitted their own - which is what I intended to do. Anyway I've found that I actually prefer it to my B17, and it has stayed on the bike. At £18 you could give it a bash, although I don't expect it to last for a long time.
But as noted above, saddle preferences are so personal as to make my waffle pretty much meaningless.