I will also add that some people here have failed to consider how demoralizing being in this age group these days is.
Uni pedaled as the key to success, so if you don't go you're a failure - well I did go, studied a 'respectable' discipline, and it didn't give me any magical happiness or means. I have a lot of debt and can't really afford any more than my peers who didn't go.
Stay at home, and be judged as a failure because you still live there, or move out and pay extortionate rent (the increase in which never shows any sign of stopping)... but then at the end of the day you're still a failure - you've never been able to afford to buy somewhere because you couldn't save. So you're stuck skint, not able to buy treats/go on holiday/go out and socialize, with £800 of your money going into someone else's pockets for years and years. Potentially forever.
Unless you found a relationship young (so you can split costs), and were lucky to find a high paying job, it's actually very difficult to know what to do for the best these days as a mid 20's person. I know because I did all the 'right' things but still my relationship ended, the market was flooded with grads, and I found myself in this position.
Is it any wonder young people are somewhat despondent? It's often not lack of ambition, hard work, or being happy to 'coast', but swimming against the tide.
If you are ok for him to live there have a conversation about saving his money. If he doesn't go out that should be relatively easy. Those who can live at home (myself included) until they figure it out are really lucky. You just have to help guide him along the way - he will get itchy feet and want to move out