Percy
Answer us this question, and perhaps we can move away from all the carping and get to the point of the thread.
Do you intend to ride more than just towpaths and gentle bridleways, or trail centre green and blue routes? Do you want to take part in MTB challenges/distance events/races, or do you want to bimble for leisure rides round the local sustrans routes?
Despite the ill-feeling, everybody posting so far is right, but are arguing from different perspectives. I agree with Zoiders up to a point, but I also agree with cjb. The willy-waving etc is a natural part of what we do as a hobby.... we love kit.
If you are only going to be doing towpaths and gentle bridleways, you don't need to spend the earth. You'll find loads of bikes at that price point, but as Zoiders says, forks at that price will be coils. If you do want to spec one, forget the groupsets (they'll all be functional but basic) and brakes will vary between mechanical discs and some rare hydraulics.
Most of the frames will be solid and functional, if not a little heavy compared with a £600 plus bike. Specialized win the frame race this far down the spec, together with the Cube analog (but that is just my opinion)
So, the fork question. Many cheap forks are undamped coils. These take some of the sting out of the bumps, but don't offer as much control as one that is well made and well damped. If you are only riding bridleways at leisurely pace, then it doesn't really matter.
If, like cjb, you want to ride faster over more technical stuff, a better fork with air spring and damping is the way to go.
Some will jump in here and say "are you telling me that you can't take a £400 Speshagiant Analock on red routes just because it's got an 80mm undamped coil fork on it?" and my answer would be, of course you can,but you will be limited in terms of speed and stopping power, and the componentry may well wear out very quickly. (possibly even as fast as XTR Angel!) What I'm trying, perhaps a bit clumsily to say here, is that I wouldn't, because I know I'd have to take it easy and would be afraid the fork would ping me off into the weeds
If you want to ride tech stuff look a bit further up the price brackets for stuff like the Carrera AM Fury. £550 will get you one of the sweetest Trail hardtails around (but you'll have to fit a 20" and be quick, there aren't many left!
If, like cjb, me and many others, you want to ride tech trails fast, and put the bike through its paces at the weekend, with a few long-distance rides thrown in, then I'm afraid you will need to spend more in order to make the experience worthwhile or enjoyable. Better brakes, lighter frames, lighter wheels, better rolling tyres, and, I'm sorry to say, better, more expensive forks. That Carrera above will do all of that for the money.
Hope this helps, but there are so many bikes out there at £400 that the choice is bewildering. Start with the fork, and look for anything with Suntour Epicon, Rockshox Dart, Manitou,. Avoid unbranded forks, and steer clear of RST. Snntour XCT or XCM are Ok, but look for ones with damping control (lockout is good, but not all that important, you don't get much pedal bob at that price point!)
If you want to do some serious stuff, spend your £400 n a secondhand bike.
Ebay is littered with unused Carreras bought on a whim. You may even find a top brand bike for littlel money, but you'll have to have reserve funds to replace worn out bits on it when it arrives.
