I honestly don't think you can buy a laptop worth spending money on for under £300 anymore. I genuinely can't recommend anything. It might be worth looking at the second hand market for example a local computer shop that is selling older machines with an i5 or i3 processor, 4gig of RAM or so and whatever hard disk. Maybe upgrade it to an SSD yourself and that would be pretty sweet. If you do that, you might ask for a warranty. CeX for example is 2 years.
Good brands are Asus, Lenovo and possibly Dell at the upper end of the range, but their aftermarket support is horrendous from what I've heard and experienced fixing other people's computers. None of them are really good unless you spend good money. It's just which machine has less planned obsolescence and compromises (mostly heat) in the internal design, which is why I like Asus, their machine seem better built and cooled.
At a stretch you could get this, looks pretty basic but it does come with a proper i3 CPU and the design is nicer than you'd normally expect from anything other than a chromebook:
https://www.ebuyer.com/767997-lenovo-v1 ... 80tl00a9ukAMD's APU (everything processor including Radeon R4 graphics) might just about manage to do some coding and compiling stuff with the 4 cores, just don't expect miracles. I would say 15" is too big to drag around though. The efficient cpu should at least give you battery life. I'm not an HP fan, their designs are bulky and cheap plastic. If you're lucky this will come with Windows10 installed or you'll have to get hold of it:
https://www.ebuyer.com/786174-hp-255-g5 ... tt38es-abuYou could actually get a Chromebook and install win10, but you'd have like 10gig of space left. Or install it to an external hard drive. The thing is they've taken the bottom end of the market in the same way netbooks/EeePCs did.