I promised a picture of the board in the folded-away position, so here it is!
The protrusion into the room is quite small - around 12", and doesn't block the window. There's space for some storage underneath too, though admittedly it isn't pretty! The black strips you can see are foam pipe lagging, to soften the blow when crawling under the layout and coming up too soon!
This is a close-up of the rear leg and the frame that holds it off the wall, the pivot bolt can be seen. Above it the front leg hangs, and in this picture the safety catch is not in use!
So base-board done there was pressure to lay some track! First the board was painted grey (with emulsion tester pots) where the track was to go, realistically ballasting isn't going to be high on the priority list but a grey base looks better than plywood. The end curves are 2nd and 3rd radius set-track and the points to the inner "loop" line are Hornby set-track, but the crossover and the branch to the upper level use Peco Streamline, and the straights are flexi-track.
There's no 3rd radius set-track point (a major omission I think), so I used a 2' radius streamline point which is a little larger in radius but flows well. The transition between point and straight, and the inner track at this location, were laid in flexi-track to match. Laying flexi-track and streamline points takes more work - trimming sleepers and carefully lining up the rails - but the result looks better and runs well too.
Much of the track came from my train-set around the loft of my parents house, it has since spent many years in their shed too, so was well tarnished, nothing would run on it. Some vigorous cleaning with a track rubber and fibreglass pencil brought back the shine and (more importantly) the electrical conductivity.
That last photo also shows the Gaugemaster double-controller set under the upper level. I wired one control to the inner track and the other to the outer track, and so we (just) had trains running by half-term!