HS2 has put in a planning application to LBH. Among other things it includes (a very unsurprising) map of lorry access to Moorhall Road and Harvil Road work sites.
The dashed line shows the routes (best to see it full-size in the third of the plans submitted) (you’ll still need to expand it to read the explanation underneath.) It’s the obvious circular route from Denham roundabout along the A40 to the A412 then onto Moorhall Road or up to Swakeleys roundabout onto Swakeleys Road then Harvil Road.
Ruislip Against HS2 says LBH is running a consultation on this – I can’t find it. I’ll let you know when and if I do.