EllisoJo

I strongly suspect that when you replaced the subframes you (quite correctly) had the alignment checked & adjusted by "professionals"
They almost certainly used the WRONG figures!
See the experiences of MGB281: I quote from one of his many posts below:

I took our TF to our local ATS and it came back darting all over the road. I took it back with the correct specs and they did it again, their database is incorrect for the TF, they claim that the database is supplied by the manufacturers of the alignment equipment. I personally think a lot of complaints of the TF being a bity darty is incorrect rear wheel alignment, we have "tested" ours on the roads and is incredibly surefooted

As you can see, it is actually a problem with the REAR end having the wrong figures in the ATS data base. I THINK I have the correct MG ROVER numbers in one of Roger Parkers books. PM me if you are unable to find the data.
Regards
John E (also in Devon BTW)