As far as I know you can use the “LAR” (local access road) all the way from Leeming to Scotch Corner … have to go through Catterick village and Brompton-on-Swale.
If coming South … come off @ Scotch Corner follow sign for Richmond (exit by Hotel) … next R/about take 1st exit ( Brompton-on-Swale) … past old Shell garage … past Chas Long new yard … follow over bridge to new R/about (TIGHT) go right thro’ Brompton … thro’ T/lights … immediately over bridge take LEFT into Catterick … follow to T- jnc by Army base … turn LEFT … follow until you come to R/about @ Leeming.
A bit complicated but doesn’t add much to journey … if A1 is shut … not sure where they sign the diversion now … at one-time they were sending you up to A66M to go into Darlington 