Not a bad suggestion, ZimZam, although the Summer heat may affect those on parade.
I have paraded at the Cenotaph for many years now, but not many people know that us veterans are already formed up in columns on Horse Guards Parade soon after 9am and have to remain in formation until about 10.30 when we march onto Whitehall to stand for the service. We then march off along Whitehall onto Parliament Square, down into St James Park and back onto Horse Guards where a member of the Royal family usually takes the salute. It can be quite a long while before the last contingent marches off from the Cenotaph .
The point I am making is that veterans can be standing still for a very long time, which is worse than keeping on the move. This is why most older veterans attend local parades where the waiting and marching times are much shorter.