rental income has to be declaredbut with lodgers, there is an amount you can make that's tax-free i think? so your DS needs to look into that.
it sounds like you need to have your name on it because of the mortgage? Or you maybe allowed to put it completely in his name. Your mortgage advisor should know the answer to this. At least they would've done 20 years ago, I'm not sure what anybody knows now!
If you do that, then he would have to fill in a tax return possibly, but he'll pay less tax than you on that rental income (depends on your income but seems a safe assumption that his is lower than yours ) so it's probably worth doing.
Then, when it comes to capital gains, according to the current situation, he wouldn't have to pay it because I presume it's going to be his only property. At the moment there's no CGT to pay on the sale of the property you lived in. If the labour chancellor decides to change that, then a lot of us will be really pissed off!
for the moment there is no CGT to pay on the sale of your own home.
Also, if your name is on theproperty, you'll be paying extra stamp duty because it will be an additional property for you - that would probably be your biggest cost at the beginning.
I think you need to do everything you can to get it in his name only, but I'm not a lawyer or an accountant or anything so I don't know how you do that. Mortgage advisor used to be really good on this kind of stuff.