Office equipment including office machinery and furniture; paper, envelopes and other office stationery; business cards and other personal and business printing
Office equipment & consumables including laminators, binders, print finishing and ink cartridges. UK delivery free over £75, otherwise from £3.95
Stationery and other office supplies including furniture. Lowest price guarantee. Free delivery on orders over £30, otherwise £3.95. 20% off first order. 
Organisers, diaries and fillers, direct from the manufacturer. UK delivery from 95p depending on order value.
Traditional office furniture and a fair selection of reproduction antique desks, chairs and cabinets. Quick delivery 10% of order value, minimum £2.80.
They source office products, computer consumables, hygiene supplies, office furniture, catering etc. from several suppliers to find the cheapest. Not the quickest. 
Office Supplies, furniture, print and computer consumables. Worth looking at for price. Free UK next day delivery on orders over £50 (before VAT) otherwise £3.95
Stationery and office furniture and equipment, hardware and accessories, but not computers. UK mainland next day delivery free over £40 (ex-VAT), otherwise £5.21. 
All the stationery and office essentials you would expect, plus a bigger than average technology section. Free next day UK delivery over £30 ex VAT, otherwise £2.90
Office furniture, stationery and other supplies including technology, health & safety, catering etc. Next working day delivery free over £40 (ex VAT), otherwise £5.95
Part of Office Depot, one of the world's biggest retailers of office supplies. Rapid free UK delivery on orders of £30 or more before VAT
Several offers for free printed products (you pay postage and VAT). Wide selection of printed items. All designed online, incorporating your own logo or picture if required.
Famous for stationery and books but also DVDs, CDs and magazines. UK home delivery free over £15, and to a WHS shop. Related pages
From envelopes to print finishing machines, if you want something for the office, you should find it here.
Office Giant have some competitive prices, so it is worth taking a look. They deliver free to the UK on orders over £35 and delivery is usually next day if you order before 5pm. Some larger things, such as furniture and electrical items, may take a little longer. Delivery on smaller orders is £2.95. In the same vein, Euroffice guarantee the lowest price, with a price-match if you know different. They also have a loyalty scheme that earns points which make prizes and free delivery on orders over £30 or £3.95 below that. Euroffice usually have a discount code, so it is worth checking the discount code page. The extra discount can be very high, typically 20% if it is your first order with them.
Staples is the world's largest office products company with outlets in 21 countries throughout the Americas and Asia as well as Europe. They have stationery, office equipment and furniture and also a fair selection of laptops and computer accessories. They deliver next day if you order by 5pm and free if your order is worth £30, otherwise there is a £2.90 charge.
Butonz supply a narrower range of office equipment and specialise in everything to do with laminating, binding and print finishing. Delivery to the UK mainland is very expensive on tiny orders, but reduces to £3.95 if you are spending over £35 and is free on orders over £75 (all before VAT).
Other specialists are Furniture at Work who supply office, meeting room and board room furniture in modern styles and in reproduction antique styles, all at a discount. They also have a 48 hour office planning service. You can collect from London, Glasgow or Liverpool or for 10% of the order value (minimum £2.80) they will deliver. Most furniture is available within 5 - 10 days, but some office essentials such as chairs can be delivered in 1 - 3 days where necessary.
Vistaprint will print office stationery, such as business cards, posters, flyers, brochures and so on. You can design what you want online, starting from scratch or using their design templates and you can incorporate your own logo, photo or other illustration. Vistaprint usually charge for the first use of your own logo or photo although they do have occasional half price and free upload offers. It is worth going for the free business cards or wall calendars (which are not quite free, because you pay for delivery and VAT on delivery) but for under £4 you get business cards and a chance to see the quality. If you like what you get, you can order other things. Have a look at the site and try out their freebies. Certainly worth trying, especially for short runs.