A colleague recently asked me for a recommendation of 'the best laptop you can buy for £400'. It's a good question, and one we are asked a lot. The trouble is there is no simple answer. (You can and should check out our regularly updated reviews and charts, of course: Best laptops for under £1,000 and best cheap laptops are important ones.)
The difficult thing about recommending Windows laptops is that they are such a commodity these days it is generally impossible to say that any individual model is much better than any other. And if it is, you never know for how long that model will stay on sale. For me, the key thing is to buy a brand, from a reputable retailer, and to look for a good specification. And the good news is that for £400 you can do very nicely. Often you can spend less.
Brand wise you won't be able to pay the premium for Apple, but should look for the bigger mass-market brands: Dell, Lenovo, HP, Acer, Asus, Toshiba etc. They are just as likely to make the occasional dud as is a small manufacturer, but they will be much more likely to solve problems after purchase. You are better off dealing with a big professional outfit.
The converse is true, of course. Find a small, no-name manufacturer and you can probably save a few pounds. Worth bearing in mind if your budget is really strapped.
In terms of spec at this price you want a Core i3 (or Core i5) processor from Intel. Because that is a CPU with a system-on-chip GPU, that hardware takes care of graphics as well as general performance, too. Only hardcore gamers will want discrete graphics on a laptop. (See also: Celeron and Pentium vs Core i3, i5 and i7.)
Software wise you want Windows 8.1 (you can save money by getting 'Windows 8.1 Bing', which uses Bing instead of Google for internal search with no discernible difference in experience).
The three key specs are memory, storage and display. You should look for at least 4GB RAM (but you can never have too much). Similarly, go for at least 500GB storage. You are unlikely to be able to afford an SSD at this price, but if you can it is a great performance enhance. So look for a 500GB, 750GB or 1TB HDD or SDD.
The display specification is more nuanced. At this price (and with portability a factor), you want a 13in or 14in display. The most important aspect thereafter is resolution. Manufacturers will skimp here. The more pixels per inch the better, in essence. A 13in 1366 x 768 display means 118 pixels per inch, which is decent for a budget laptop. And try to get matte rather than glossy. Glossy displays can be horribly reflective. And a touchscreen is a luxury you don't need at this price.
That's about it really. Buy using a credit card because it gives you additional protection if something goes wrong. Do buy third-party antivirus, but don't be upsold on warranties or software add-ons. And buy from somewhere with a street address and a Companies House listing.