It is not an easy job to replace these - would need a large number of 8x4 dry lining sheets removed. No option to remove floor above due to underfloor heating
I have drilled in a new hole in timber frame header (horizontal) to allow reroute.
The is not enough slack in the singles to do this .... and easy solution would be to cut each single and splice in a 12" extension. I can make the cut so this happens above the header plate, and it can be clipped to joist for mechanical support.
The splice ... is it acceptable to solder connect ? .,.... I could solder, insulate & sheath with double layers of heat shrink, and mechanically fix .... simple & neat. Is this acceptable under 17th Edition ?
Not that any inspection taking place .... but prefer to do things right.
Alternative but bulky & not so easy is to splice in with 2 x Ashley J804 junction boxes.