I can really see both sides of this.
I have never tied pocket money to chores, as I feel that they shoudl help around the house because they live in it, and help to make the mess.
I have always felt that by linking it to pocket money you take away the idea that they should be taking responsibility for keeping their environment clean and tidy.
On the other hand work = money in the real world.
We have certain chores that have to be done. If they don't do it, there are consequences. No screens, removal of phones or removal of pocket money. Once the chores are embedded in routine we find they happen, introducing new chores is always a nightmare.
Then we allow them to earn extra pocket money by helping on less regular jobs - mowing the lawn, cleaning the car etc.
Reading your last posts, I would remove x boxes altogether, and they only get them back when they have proved they will do chores and as soon as they slack off, the x box goes. I think with these sort of things there is no discussion - I really don't care how your friend's parents do it, in this house everyone pulls their weight. Help, or you loose your screens. At their age I would be hard line with getting that attitude.
The amount of money really depends on what they are expected to buy with it.
Notso - £130 per month

If they aren't buying clothes or bus fares then £5 is fine. Give according to what you have too.