If your partner moves in with you and only contributes to half the bills, his amount of disposable income will increase much more than yours as a result of living rent free in YOUR property (whereas, as you say, you won't benefit anywhere near as much as him).
Everyone should expect to pay for their accommodation as well as the bills.
If you split up in a few years' time, how would you feel about how the finances had been split (and how much he'd benefitted compared to you)?
I'm in a similar position to you. If my partner moved in with me and we just 'split the bills', he'd be gaining massively financially from my 25 years of working hard to pay off a mortgage (in a time that we weren't even together).
You should split the 'benefit' so maybe charge him rent (£350) until you're both contributing to a joint property.
Carefully check the laws around your future living arrangements and the circumstances in which he could make some sort of claim on your property.
Protecting your assets isn't a very romantic topic but if your relationship doesn't work out it WILL all boil down to money and practicalities.