Solo - Nothing is free fgs, this is the real life lesson, not 'don't worry son/daughter, you can live here for as long as you want, mummy will look after you'.
That's a ridiculous assumption. All my kids more than pull their weight when living here. In fact, I'm pretty sure I get more out of the deal than they do these days, in terms of help with the garden, lifts for younger kids and DIY around the house.
I was kicked out at 16 and had no family support at all since then, neither did my siblings - so I'm very aware of 'life lessons' thanks - and the toll it takes when young people are not fully supported in early adulthood. Let's just say it took some of us a while to find our way. I didn't want that for my kids. They go when they're ready, and if they need/want to come back, that's fine too. (It makes no practical sense for a huge FO house to be half-empty while the kids scrimp for rent.) And surprise, surprise, the ones who have left are more than capable of holding down good jobs, paying rent and mortgages, and turned out to be generally fully-functioning members of society, without me needing to teach them additional 'life lessons' about rent.
£7500 p.a. is only £625 a month. If you're talking 2 or 3 adult children being charged £250 p.m, as some posters have suggested, you're already over that.