To think he should pay more board?

Surely it depends on how much he receives in benefit?

It doesn't sound like this is a sustainable arrangement as you sound quite resentful (not being unkind, it must be tough!)

I think £50 a week from the limited income of benefits is reasonable depending on whether he buys his own food?

How much does he get in benefits à week ?

He pays to rent space in a shed?

I think £55 per week from someone who receives sickness benefits is a fair amount.

And I wouldn't be looking to grab some from his PIP or ESA added element.

What does your DH say?

It was bought especially for him so why not?

Can you change it to be a percentage of his income. So rather than a set £50 it's 15% or whatever. That way if he gets more money the actual amount goes up because the percentage stays the same?

I'd discuss it with your DH though as it's his son so it needs both of you on board.

Aside: what does he own that requires a whole shed?!?

£50 a week is a lot given he's on benefits. Are there increasing costs you need to cover?

Is this a reverse OP?

A shed needn't have cost nearly £700 that was your choice, £55 a week, £220-£275 a month from ill health benefits is quite a bit , it does seem that you resent him.

Saying that, I've just reread and realised that his money increased due to increased needs, so I wouldn't be looking to up his contribution if the extra benefit is to help pay for eg disability aids or whatever.

20% of what he gets

But you didn't need to buy a £700 shed

Actually I think you are being a bit tight. What does dh say?

I've got adult sons living at home, and depending on what and how much he eats, £50 would cover food and toiletries, and a contribution ( not much of one) towards bills.

My other son rents a flat, his bills come to about £200 pm on top of rent, maybe more if you include council tax. That doesn't include food. If you include utilities, broadband, increased energy bills because he's at home all day, along with food, then I reckon £50 is nowhere near enough. If you have to pay rent as well, then that should really be reflected in his contribution.
It really depends whether you are happy to subsidise him or whether you want him to pay a proper share of the household expenses.

It would be more reasonable (and helpful for him tbh) to be looking at this in terms of what he has coming in, what that can be divided into (room and board, personal care, spending money, savings for example) and work towards getting him budgeting and considering how he uses his money if he's ever going to move out.

You agreed on a fair amount when he moved in - what's changed about your income/outgoing balance that's prompted the thread?

If my adult son was struggling with MH problems and living on benefits, I’d feel £50 a week was quite a lot to be charging him I think.

I think the bigger issue is that you seem to feel resentful of the arrangement. Can you re-evaluate whether the arrangement is working?

I think the amount he pays is reasonable considering he's on benefits. You've mentioned that he's had an increase, but that's due to needs based not living costs so obviously he needs is for other things based on why he was given the extra so I don't think it's reasonable to request more.
What does you dh say?

How old is he? Guessing early 20s, in which case I would give him a break as he is saving and paying for driving lessons.

£220 a month when on benefits is more than reasonable. You sound very resentful of him living with you. The shed is ridiculous. If you didn't want to buy it you shouldn't have. Moaning about the room it takes up is petty.

Not only that, but the space it takes up in our garden is space we have paid for and can't use

that sounds really petty.