Canon EOS 5D Mark III 22.3 MP Full Frame CMOS with 1080p Full-HD Video Mode Digital SLR Camera (Body) Canon DSLR Camera [EOS 90D] with Built-in Wi-Fi, Bluetooth, DIGIC 8 Image Processor, 4K Video, Dual Pixel CMOS AF, and 3.0 Inch Vari-Angle Touch LCD Screen, [Body Only], Black
Price comparison. Canon EOS 5D Mark II. JINTU 85mm f/1.8-F22 Portrait Aspherical Manual Camera Telephoto Lens For Canon EOS 5D mark iii ii 7D ii 6D 90D 80D 70D

The Canon EOS 6D is available for £1599 body only, this makes it rougly £700 cheaper than the Canon EOS 5D Mark III, leaving you a decent amount of money to spend on a lens.

Canon EOS 5D Mark II Canon EOS 5D Mark III Canon EOS 6D Nikon D600 Nikon D800/ D800E; Sensor effective resolution: 21.1MP CMOS Mfr. price: $2,199 (body only) $3,499 (body only)
Guaranteed to operate with your Canon LP-E6 LP-E6N and LP-E6NH cameras including the Canon 6D, 7D and 7D Mark II, 70D, 60D, 5D Mark II Mark III and Mark IV, 80D, 90D, and EOS 5DS R R5 R6 R7 DSLR Cameras, replaces the Canon LC-E6 Charger.
When light levels get low, the EOS 6D keeps delivering superb photography. ISO sensitivity extends from ISO 100 up to ISO 25,600 (expandable to L:50, H1:51,200, H2:102,400) and an 11-point autofocus system is responsive down to -3EV. That’s sensitive enough to operate under moonlight. hIbq.