Bought the computer a couple of years back and have already had this problem fixed under warrenty - obviously warrenty is no longer valid.

Knocked the computer a couple of weeks back, only a gentle tap with the back of my hand (I was turning to face my desk). I now have a prominent green line down the centre of the screen. It is not pixel related and is therefore the screen that is at fault.

If I pinch the top centre of the frame the line dissapears? But comes back when released

I have investigated, checked ALL connections but to no avail. Any help will be much appreciated!!!

as you have guessed the screen is knackered.
you can check this by connecting to an external monitor
and using Fn plus one of the Function keys on top of keyBoard to throw the picture to external monitor.
the only possibility is to go back to place you bought it with
the history of the same repair , and point out that the repair was not done properly as you got the same fault back
or else the goods was not fit for the purpose it was originally sold to you ,as within a year the screen goes and their repairers have done a gudge job.
see what the manager says??
the repair is expensive, so you are better off buying a new one rather than repair.
the manager might offer you a last chance repair or might say he will discount so much of the price of a new one.

Advent Laptop repair
or get an estimate ffor the repair