Hi
Apologies if asked before but I can’t find anything when I search.
If I order in a Saturday before 3pm will it be delivered Monday?
Don’t think so , think it’s based on standard working days
Correct. Tuesday would be your delivery day.
Source: Personal experience. 
Sadly not yet.
Just for future reference all in the info is in the footer of all page of the main site:
Free delivery to mainland UK only. This does not include the Scottish Highlands, Scottish Islands, Northern Ireland, Jersey, Guernsey or the Isle of Man. We also deliver to all of Europe. If you order before 3pm it will be delivered the next working day. We don’t pick and pack at the weekend, so if you order then it will be picked and packed on Monday and delivered on Tues.