Here we go with the 'but but but.....' It's just excuses excuses........... It doesn't sound like the OP's son has even TRIED to get a job. And even if he had and cannot get a job, he can hand over the bulk of his benefit to his mother (the OP,) and not dish out a paltry bloody £50 a month of it.
He has over £200 surplus income - a month - to sped on frivolities and jollies. He has no bills, no rent, no insurances, no food to buy, no travel expenses as he has no job, and he doesn't even pay for his own mobile phone! His mother pays for it! Most people don't have HALF the surplus income that he has at the end of the month. No excuses for the OP to be £300 a month worse off when her (now adult) son is getting £250 a month. Get him to hand the bulk of it over til he can be arsed to go out to work. Why is the OP bankrolling an adult?
As some posters have said, the casual jobs to bring in some dosh to help out, are out there in droves. Some people just CBA to look! The OP's son sounds like one. He is a fussy eater too, and as I said, she pays his bloody mobile phone bill. Time for this young man to step up and for the OP to stop coddling him.
I'm not saying 'woo hoo he's 18 he can leave etc. But he can look a bit harder for work, AND pay for his own phone! And also - as for the fussy eating. Fuck that. It would be 'you have 2 choices... eat or starve.' FFS the pussyfooting around and mollycoddling that is being suggested on this thread is breathtaking. No wonder SOME young people are like they are. I think you know what I mean!!!