The HP EliteDesk 800 G2 Mini desktop is now available on eBay.co.uk for only £455 GBP (free shipping in the UK). The model # is L1W21AV and the deal includes HP's keyboard & mouse.
This particular item has the DisplayPort + VGA + HDMI option, 2.5GHz-3.1GHz Core i5-6500T CPU, 16GB DDR4 2133MHz RAM (2x 8GB) and a 2.5" 500GB HDD. The built-in HD 530 GPU is quite capable as well.
You also get Windows 10 pre-installed with a downgrade right to switch to Windows 7, if desired.
The possibility to hook up 3 monitors (at the same time) to this little machine is very useful as well.
Worth a buy, if you ask me.