UKH

This area looks like another minefield ?

Buying  Hiking glasses ( I already have a set of goggles ) but are the cheaper glasses say from £2 to £10  vastly different from the expensive names like Oakley or Julbo , what is/are a good pair without  paying 1   or 2 pounds ?

Look up "bolle spider".

No they are much the same and you don't mind when you lose/scratch/break them. Look for the darkness category.  As long as it is 3 or 4, they will do the job.  Try Decathlon (and maybe £15).

As long as they are CE marked and cat 3 (normal sunglasses) or cat 4 for glacier type stuff you shoyls be fine. 

Robustness is the main thing I've always looked for. Bolle have polycarbonate frames so I have used these exclusively for the last 20 years or more. Each pair copes with about 5-8 years use being crammed in my pack and head on the mountains for weekends and holidays, plus being crammed in my school bag and being worn literally every day of my life. After 5-8 years the lenses are a bit worn/scratched, although the sunglasses are still wearable. They cost about £55-80 each depending.