Yes, I can reduce the length of my tandem (converted Moulton ATB) by detaching the front section, but wo+manhandling the two parts would be troublesome, especially if stairs were involved.
I'll stick to using the car for transportation! We normally head out of town rather than in for rides.
I do take solos on the tube, just have to avoid the deep tube tunnels and weekday peak hours.
It's a pity that no bicycles will be allowed in the central Crossrail tunnels either, despite the tunnel walkways provided for train evacuations.