May I suggest you have a look at this sub-forum (to which I asked the mods to move your thread). I think there'll be more 'knowledge' there than from the few who choose to look and offer an answer to the Q: best MTB for £200.
I suggest you need to think what surfaces you are mostly going to use your new bike on. Nearly all MTBs will come with a suspension fork (whether they need it or not) and also knobbly tyres (which are a bit of a pain if you're mostly going to be on tarmac).
@DCLane has suggested the Carrera range (think
Halfords) so I'd go and have a look online and in store, and in your local bike shop (LBS). Finally much better value for money is likely a second hand one, and again some LBS have a few outside (mine does). Also if you get in touch with your local cycle club, you may find one of the members has a bike for sale.
I'd hope to get an alloy (ie aluminium alloy) as opposed to steel frame, 3 x 7 or 3 x 8 gears, and trigger shifters (ie not twist grip).
I assumed you wouldn't get disc brakes at that price point but this one has: m-trax-by-raleigh-graben-29-er-mens-mountain-bike but 17kg! (how do they manage to make it that heavy?) This is not a recommendation for this bike.