He could have previously set his rates at £60 based on the job at the time and the customers circumstances.........not entirely fair but it is possible.
Does he keep accounts to make a record of jobs he has done, what he charged etc? If not, why don't you suggest that he does exactly that? He should be declaring all his earnings to HMRC anyway.
It would be a shame to end the relationship over what I think is a paltry sum........£60 a day is peanuts to be honest. Do not make any hasty decisions and spoil what could be a lovely relationship.
He has helped you, now you help him, support him to get his 'odd job' business on the right footing, proper accounts, decent earnings and a competitive but fair pricing structure.