Thanks for the ideas guys.
The inflateable bags are an idea but after a bit of searching i saw a couple of clips of them and the use of them is cringe worthy.
smashing a window does seem exteme but i would be the cheapest way. the cleaning... well I think I could manage that would leave the car cleaner than now as id take the seats out to get into all the nooks.
I wouldnt wanna smash the interior becase the full mj trim and carpets.
Thankfully the previos owner called me to let me know that they key is the correct one for the boot.
I didnt wanna force the key into the lock, so thought it was the wrong one
I've freed the lock up abit with some oil but to be fair, WD would probably do abetter job so gonna get a can in the morning and have another go at getting the key into the lock and unlocking the car.
So theres hope of getting into the car without damage.