Lovely S1.
I had DVLA issues also. The previous owner had taken the S2a along for MOT for over 10 years to the same place, and it seems that they hadn't picked up on the error recording the VIN number with an E instead of a B suffix.
Thought I was going to have a nightmare with DVLA, but it was sorted out fairly quickly with an independent inspection letter.
Hopefully you will get things sorted quickly.