1 How would the Police cope
Badly, they would need the support of the Military who would I guess would deal with things much more firmly.
2 How could the govt cope cos with only 82,000 troops they could not control even a 1/4 of the country
I think the issue is that the numbers of rioters etc would be relatively small and as seen in Tottenham, I think communities would come together to protect their own property and families.
Also this sort of rioting is normally restricted to the large conurbations/cities
3 How far would the economy fall apart and could it recover quick enough to prevent a major national catastrophe.
In this aspect, if we are talking about a UK only situation, then I think(?) that we could recover quite quickly, a lot of trade is international these days, and dare I say it, but the results of the riots just like previous flooding events would actually create a boom time for builders and tradesmen, both through repairs and rebuilding, and also from others who want to introduce more protection to the their properties...
4 How could we plan and respond
Don't live in Cities
Of course all of the above could be way of the mark