OP, this is an excellent question.
If you're not trolling but genuinely want opinions on situation, try to imagine and honestly answer this. Your brother has £10 extra per day to cover everything related to your niece, and is a solo parent to her as well.
He's late to collect her from the nursery? £10 lateness fee, and he's in the red for the day.
D&V episode, and the nursery excludes her for 48 hours? Very sad, very sad, the emergency nanny starts at £150 / day. Alternatively, your brother's patients don't get their surgeries (substitute with whatever his profession is).
He wants to go and watch football with mates? £40 in babysitter cost to cover the match time, getting there and back. No-no to a pint after, the clock is ticking.
A smoothie and a sandwich in the softplay? £10.
Invited to a birthday party? Another £10.
Grew out of her car seat or buggy? £300 boom, that's the months budget gone.
Something seems wrong with her teeth as they start growing? The NHS dentist will see her when she's 45. Or £150 a visit for a private one.
And ALL of the above will be only his problems to organise, pay and follow through.