Can you send an item by royal mail special delivery on a Saturday, to arrive on the Monday?
I don’t think Royal Mail include Saturday as a business day for the terms of guaranteed delivery so it may still get there but won’t be guaranteed until the tuesday. Available six days a week You can use Special Delivery™ Next Day from Monday to Friday, except bank holidays or public holidays. If you need your item sent over the weekend, you can also arrange a guaranteed Saturday Delivery.