As I said, I'm no bicycle expert, despite always having had a bike. I just took whatever I've been riding for granted. I've had one new bike in my life - a thing with small fat white tyres my parents gave me for Christmas when I was about ten. Then I had my bro's hand me down - a proper adult 28" bicycle, and since then it's been second hand Malvern Stars, etc bought from the paper and ridden until stolen. I'm a bit mechanical, but my cycle mechanics has been limited to taking everything I can off whatever bike I've had. Just the frame seat, bars and wheels thanks. I did once buy a SA ABC (?) hub and amused myself by relining the tiny brakes with little pads sand rivets. I got a beautifully lugged old frame and tried to build up a bike (like the beautiful 1958 Raleigh Sports I've just bought, which I won't be stripping back), but the wheels stumped me and the bits were lost in house moves over the years. I've still got my lovely shiny hub with new brake pads, though.
Only lately I've discovered how cheap used bikes are, and the joys of having a stable of mounts. The pleasure of choice!
I've read about old bikes, and was surprised to see how 'modern' the Rover Safety Bicycle (?) looked, or how old looking modern road bikes at least are.
I'm taking the barn find very seriously. Some of the bikes look very old, and as mentioned I will carefully log them before deciding what to do with them. Soft sucker that I am, I want to involve the 75 year old shed owner in the outcome if there really is something to be made out of them.
I also want to find out what on earth they are all doing in a shed at X-----.

Someone must have collected them.
Thanks for those URLs - I'll definitely follow them up. I'll need the help, and thanks all for the help so far.