Why is it zero?

The government should transform the life chances of disadvantaged families first, making sure childcare and early education are good quality and affordable.

We also need to make sure that Universal Credit allows families to afford the essentials and scrap the two-child limit 3/3

In fairness, I think the Tories should've been given more time. 14years in power just isn't enough.

👆 Sarcasm BTW

Those rules apply regardless of age.

Yep, i've been through the PIP appeal stage with my Mum so know all about the scoring system.

Does your brother meet the criteria for the high disabilty payments he receives?

You originally said "More people than you realise have more disposable income not working than doing so."

For that to be true you need to compare a person being in work to the same person not in work.
All you're doing is comparing 2 different hypothetical people with different circumstances.

Might be better to leave current SP claimants as they are but then people reaching the pension age could claim (or stay on) Universal Credit. SP would then be gradually phased out.
Obviously it'd be at an enhanced rate with a few different rules/thresholds but it could definitely work.

Why have 318,000 legacy benefit claimants not gone on to claim Universal Credit?

This is for the Person A.
Circumstances are same as person B except for the disabilities.
So person A is about £1000/month better off working than not.
And person B is about £1000/month better off in work than not.

You were talking about people being better off in work than not.
So are we talking about:
Person A who receives £30k in benefits
or
Person B who is in work earning £30k and not disabled?
(I've already proven Person B is significantly better off in work than not)

Sorry, forgot to add the screenshot from an actual benefit calculator....

That's not how benefits work!!!
Calculation below is based on 35yr old adult with £700 monthly rent.
'Current income' = unemployed
versus
'Income in work' based on £31,200 salary

£935 per month better off in work.

If the £30k worker lost their job would they be better or worse off?
If the £30k benefit claimant found a job, would they be better or worse off?

How many is it?

Can you give an example of when someone would be better off by not working?

Apart from very few extreme fringe scenarios, it's better off to work than not.
In your example you're comparing apples with pears so comparisons are quite meaningless.