Not sure which Flexicrew contract this is from, but it's not the one the I've seen....
Under the old contract, a fixed amount was paid per day as holiday pay, thus removing the entitlement for paid leave- leave was accrued, then taken unpaid.
Apparently this is no longer legal, so under the new contract, paid holiday is accrued and then taken whenever you like i.e. work 10 hours, you accrue 1 hour paid holiday.
Sounds like there a different versions of this contract for different groups.
FYI any clause that states you cannot take holiday in a certain period invalidates the contract as a true 'contractors' contract, as to be a contractor you must have complete control over your own working hours etc etc, so good luck anyone trying to pull an IR35 breaking 'self employed' scam...