I’ve had advice from the Royal Mail that they are not currently able to guarantee that their Special Delivery Next Day by 1pm service will actually arrive the next day by 1pm.
To save customers any frustration I have decided to remove this option from the checkout temporarily, and when the Royal Mail say the service has returned to normal it will become available again.
My apologies that this will impact on some people that need an order in a rush. There is still a next day service available in the form of RM24 (which is tracked on all packages, which are most orders that aren’t books), but this isn’t guaranteed.