Jos, Not quite. Official flags follow the rules of heraldry, and one of those is that you can't have white against yellow, nor can you have any of the other permitted colours (red, blue, green, black, and purple)against each other either. There is just one special exception - the papal arms which are yellow and white (or gold and silver, since no doubt the R C Church can afford it.) The reason is visibilty. In the melee of medieval battle when you're trying to see something through the bars of your visor, you had to be able to recognise instantly friend or foe. That is also why the colours are all primary; no pink or brown or grey.

I doubt that the Cornish would welcome being represented on any future flag as most of them don't think of themselves as English anyway.

As for a public vote .... of course the govt would veto it. Any decision like that would need the approval of the queen anyway, and that would most certainly be the case for the coat of arms as the UK's are the queen's personal arms as well.

I should say that I was going a little off-piste in my last post as I really had in mind coats of arms (i.e. shields, crests etc) than flags. Crosses or tricolours certainly suit flags better than animals.