Post edited 10:38 – Dec 25th 2016 by No1Spank
Sorry it's a bit late in the day to make this Xmas.
If you haven't bought one yet make sure it has a quad core processor not an i3 dual core with hyperthreading or an AMD FX #### as both will struggle on high end triple AAA games. 6 core & 8 core FX processors are ok though.
You want 2gb absolute minimum graphics memory but 4gb would be a lot better. A GTX 1060 with 3gb of memory would probably be the best card you could buy on your budget having said that.
Memory wise you will need at least 8gb and a solid state (SSD) drive with at least 240gb would be good.
Also a decent quality power supply (PSU) from a brand like Corsair, Antec or Thermaltake etc.
Any speakers will probably do but I like logitec myself, a nice 2.1 kit is about £45 online (ebuyer).
I've no idea when it comes to head phones, I have some cheap ones from Tesco which give reasonable sound but hurt my ears after a while. Anything that will plug into the headphone jack will work.
I would steer clear of places like PC world as they will punt out the absolute minimum for the price and fob you off with sub par parts claiming they are gaming quality.
There are companies online like Scan or YoYo Tech that will build a gaming rig to the best spec possible within your budget.
Screen wise I still use a 21.5" widescreen I got from ebay for 35 quid which came with a cheap mouse, keyboard and speakers. It's resolution is 1650 x 1050 which is plenty good enough for my eyesight (not that much lower than 1080p) although you might need an adapter if you get a HD graphics card. I got one for mine which was about 6 quid on ebay.
These days a reasonable 22 inch 1080p monitor is about 80 quid new, don't get a super cheap mouse or keyboard like xenta as bad ones can short out the USB controller. Stick with brands like kingston or logitech or others in their price range, they are still cheap enough and 25 quid should easily be enough for both.
If you could sort the screen, speakers & keyboard etc I'm sure someone on here could build you a good spec machine within budget. Don't you have any mates who are PC builders?