Pop your seat off Guys and check the 10 mm bolt that secures the seat lock, mine came loose the other day the result was I couldn't remove the seat.
I spent the afternoon today trying to access the lock which is difficult but can be done by forcing the seat out at the front which allows you enough room once prised up to remove the right hand rear side panel.
Once this is off you can unclip the undertray enough to get a screwdriver in to release the seat lock.
Sorry should have thought to take some pictures but hay ho if you make sure the bolts tight you shouldn't get this issue.
I've put a drop of thread lock on the bolt to stop it happening again.