As for "why cant more staff be rostered" etc, the rosters are worked out every May and December, on Sunday 20 May 12 I started work at 0810 and on Sunday 02 December 12 I will start work at 0730, that is how it works, extra staff cannot be forced to work just because there is some do or other going on in London.!
That's interesting, I had no idea that they would be done quite that far in advance, so that does explain how hard it must be to make amendments further down the line.