The twin and earth will be fine in the loft (outside the lagging insulation) with no further protection other than its outer jacket, if you can route it in such away it cannot be mechanically damaged by the normal moving of 'stuff' likely to be in a loft. (The same is true of a lighting wiring), so if its clipped neatly to the sides of the joists, or to battens attached to the sloping bits (come one someone tell me the proper name for this) and crosses joists only in places where it cannot be trodden on or pinched, then you have no problem.
Otherwise yes, if it can't be routed safely, then protect it.
Usual cause of accidents is if the loft is floored out and cables that were obvious to the original installer are suddenly crushed beteen floor and wood work suffering in the darkness. (lifting the floor panels on battens omnn the joists is a partial solution, but you need to mark it "cable below " as the cable will not be deep enough below the floor to avoid being nailed so it is not a proper installation method.)
If you must keep the 1mm spur from something unsuitable, at leaast add a 3A or 5A fuse in line, though ideally transfer it to the nearest lighting circuit feed, probably L and N at the nearest ceiling rose.
regards M.
