Okay, so I now have a new question for you all.
I just got into the car to turn it over, it has been stationary for 4 days now since it got stuck. I put the clutch in, started the engine and just for good measure gave the gear stick a quick wiggle, and well... it came straight out of reverse and I was able to select first and away it went.
Now, originally I thought the shifter had gone into neutral and left the box in reverse. However clearly it was always in reverse but felt like neutral as there was so much movement. I have no idea why suddenly it decided to come out, but I am bloody happy.
My actually question is why is the likely cause, and what can I do to prevent it happening again?