If you want to buy new, there's a few "builders" in the UK who do great deals. In some ways better than the big brands (specialized, trek, giant etc), because you get better value for money. IMO the brand thing is a fudge, because - say - specialised... - what is actually MADE by specialized - the wheels, gears, brakes etc are usually bought-in (shimano etc), and only the frame is manufactured by specialized...and that will be made in taiwan anyway! Plus the big brands are notorious for putting cheapychinky components where you don't see/notice them (like the bottom bracket).
Therefor I would recommend something like:
https://www.ribblecycles.co.uk/ribble-hybrid-al/
This would be speedy on tarmac, and well-kitted out. You could ask them (as others recommend) to swap the saddle...
Nearer you is Planet-X, they used to do a "London Road" with flat bars:
https://www.planetx.co.uk/c/q/bikes/road-bikes/london-road (but I can't see it now)
Merlin is another "builder" -
https://www.merlincycles.com/ - these 3 (Merlin, Ribble, PlanetX) compete vigorously so you can be sure to get a good deal. Prices will be on a par with Decathlon and Halfrauds but you'll get much better service
You get the same Shimano gears, bought-in wheels etc as a specialized/trek/giant, but for less cash...