Just to touch on this topic again if anyone needs similar help in the future.
Didnt get a new windscreen in the end after a botched visit by national windscreens I told him to return to his van and leave - awful company to deal with.
Searched and called many companies and came across Glasweld . Called and oragnised the local tech to come out.
Bear in mind my nail did catch on the scratch.
He look 10 seconds to confirm it will be sorted within an hour. They use some kind of water cooled glass displacement machine? Dont ask me too much detail. Basically you dont remove any glass at all you it just 'displaces it back to place'
Anyway, 1 hour later, scratch is completely gone, absolutely no distortion in the glass what so ever and for under 100 quid Im over the moon.
Running my nail over the area he worked it is smooth as new, no dips in the glass at all. whatever they use it works!
Also speaking to the chap he told me you wouldnt belive the amount of work they do on brand new cars when they turn up from the factory. Apparently side windows and windscreens get scratched all the time in transport. A lot of their work is through dealerships.
The work does create a mess, compound everywhere so a good clean after is essential.