UPDATE - if anyone is interested!!!
Today I called into a national widowscreen replacement firm.
The chap looked and agreed the scratch was into the glass but said they do not polish out any more as the polishing weakens the glass and given the place may/can distort the view which may contribute to an accident.
Apparently there have been a number of legal cases and so they will not polish to prevent any such claims against them.
As it wasn't in my direct view, as on the passenger side, it shouldn't fail on the MOT.
He did say I could replaced the screen if I wished, £60 excess, as he spotted a few chips, again not in drivers direct view, and suggested I wait until nearer the MOT date and he will check it over again.
He also said there are 2 types of screen available for the i30 (I think he said both are made by the same company) - Hyundai sourced and generic sourced.
If I want Hy sourced this would take an extra week as they will need to order direct rather than "off the shelf".