Yeah, Hardrock is pretty average. But, if all you want is an old-style MTB to pootle about on and it fits, then it needs to be quite a bit below £100. It does have the reflectors so it might actually be in really good nick - these were usually quickly removed! We'd need a photo of the other side to see if the drivetrain is shocking, or OK for the money. Those shifters look 'funny'.....as for year, I'm no expert, but earlier part of the 90's I should think.
Put a wanted ad up on here - maybe stating your budget/ what you want to use the bike 'for' and where you are - you might get something nicer and hopefully well looked-after.