Of course, you also have to bear in mind that 911 was the main emergency number in the US well before the advent of 9/11, (or 11/9 – whichever you prefer) and there was always speculation that the date was chosen for exactly that reason.

As a result, I suspect there might be a few security agencies wondering whether 9/9/9 might be planned to be of similar significance/utilityin the UK…