Top Contenders would be:-
Seasonic X-850 Â£155.98
Corsair AX850 Â£142.60 7yr Warranty
Corsair HX 850 7yr Warranty Â£123.95 (slightly older unit but fantastic performer and long warranty)
XFX Pro 850W 5yr Warranty Â£95.82
Almost forgot- NZXT Hale90 850w Â£134.36
Older XFX 850 XXX editions (luminous fan) were top notch too, might aswell get the newer stuff though.
Me personally, I'd go for the Seasonic X-850 or the AX850 if I had a full 150-160 to use.
Had my heart set on the HX for so long, fantastic performer, it's so closely priced to the AX and the AX is fully modular, so matter of perference, if my max budget was 100 quid, the XFX for sure.