This tech tip is bestowed upon us from the MG factory. Refering to Confidential Service Memorandum MG/358 dated 24 March 1962.

If the surface of the transparent flexible sheet is not too badly damaged, the surface hair scratches may be removed in the following manner:

Using a soft sponge, wash with soap and water, rinse with clean water, and dry.
A smear of hard wax polish should then be applied with a soft moistened cloth, to give a veneer of wax and fill the scratches.
Finally polish with a soft duster.