When I was looking for a good chair I thought about the DX Racer. I really wanted one but looking back I'm kind of glad I didn't get one they seemed a bit to exaggerated. I ended up getting one from amazon, that to this day I really like. it's kind of big and "bulky" but pretty damn comfortable where I can easily sit in every night for 5+ hours.
A big problem I think is that DX Racers are mostly given to streamers/youtubers for free or at a very discounted price and one can't complain about something free.
This is the chair I got. https://www.amazon.com/dp/B007N134L6/ref=cm_sw_r_cp_apa_s4EuybKPJ24NQ
Although I am not super expert in this field but, I have two recommendation for you, its under your budget hopefully it would be comfortable too (based on customer review). first one is Flash Furniture Vinyl Executive Office Chair and the second one is Flash Furniture High Back Leather Chair. didn't search at UK market but Flash Furniture is a big brand and I am sure they have covered their UK market.
I'm eyeballing this one, my buddy just got it so I'm waiting to hear what his impressions are in 6 months or so to make my decision.
haha sorry guys been away from reddit for a while the chair is: http://www.amazon.com/Flash-Furniture-CH-CX0248H01-VEN-GG-Executive-Pipeline/dp/B007N134L6/ref=sr_1_6?ie=UTF8&qid=1427161790&sr=8-6&keywords=red+gaming+chair