Does anyone know the current building regulations regarding minimum
clearance needed when installing a space saver staircase into a loft
conversion?

You need 2m directly vertically above the stairs. You may be able to
persuade the BCO to accept 1.9m above the middle, and no lower than 1.8m at
the side.

You will need a landing at the top, usually 0.8m x 0.8m.

Christian.