Penny Red George V

In my youth I collected stamps. They are all in a bit of a jumble and a few weeks before Christmas I spotted a "stamp fair" at the local scout hut on a Sunday.
So I popped in to have a look and explained to the organiser who was very helpful and said to bring the collection in and he would appraise it and suggest a way to bring it up to date.
The next meeting is this coming Sunday, so I had a spare hour today and thought I would familiarise myself with exactly what I have and am trying to achieve.
I do believe the King George V penny red is one of "those" stamps that might be worth a bit of money. Of course it might not be, but I will report back on Sunday, if I am still here and haven't flown off somewhere exotic.
What are the chances of that!!