As others have said, it isn't up to your dad, it's up to you. It sounds as though it's a formal arrangement you have with your friend, which could pose a problem - as Ishyan mentions, if you care for a child for more than 2 hours, you need to register as a childminder (regardless of if there is any financial payment happening incidently).
A friend coming over to play is different as it isn't a regular formal arrangement, but you say you are providing 10 hours per week, so I would suspect that you could be pushing the rules a bit - if you are in England. If you are in Scotland, Wales or Northern Ireland - or anywhere else for that, you will need to check local laws.
Having a friends child come over every now and then I would say is not uncommon - it's good for children to socialise and helps give another parent an hour or so off... also helps to know other local parents as you can then get the favour returned, so you get some time to yourself.
Having a regular agreement, such as I suspect you have, I would say is uncommon, unless you are a Register Childminder or Approved Childcarer(Nanny).