You need to open the boot take the black plastic cover off to reveal the locking system and spray wd 40 onto the locking system and keep pressing the button to work it in... Had the same problem last year.
this was the problem i had when brought the car, me and my dad completely ripped out the motor and mech and stripped the mech apart and scraped all the rust of and rebuilt it. Before we put it back together we packed it with grease. Now it works fine and has done for a whole year lol.
Pull the plastic cover off the boot part. Look at it from behind and you can easily see the catch mechanism. Use a screwdriver to press the catch up and see how much movement there is in the lock that springs across.
The mechanism is awful. It's too flexible and I think the spring has a habit of stretching.
Get some WD40 and operate it a few times whilst you watch. It may fix the problem or just offer a temporary solution.
If you keep slamming your boot hard it will make it worse !!
ahh poo, mines broke too and have been just slamming it shut for the last couple of months,i took it to the mg garage by mine aswell and he didnt seem to know what to do,he messed around with it a bit and it did work better for a while but its really bad now, will i need to replace it do you think?