Righto - got into the bombardment, the Allies started knocking a hole in the curtain wall. I think that in the real WSS the French garrison would have surrendered by now, but in the interests of testing most of the rules I have pushed it on.
Some interesting bits and pieces along the way; since the changes in the artillery rules, the only decent strategy the defenders had against sapping was to use lots of Trench Raids, which is entertaining, and they did pretty well - they were a major nuisance, they killed some sappers, and supporting infantry, and they eliminated one of the Allied guns [they didn't take the thing away, they spiked it].
The Allies found out that their spy (code name Heinrich) was of good quality, so they directed him to have a go at damaging the town's flour store, and he did it so successfully that the garrison commander lost 8 turns of food, and the situation started looking critical. The French Governor took some of the steps available to him to make the rations go further:
(a) he reduced the standard rations, which added 10% to the number of turns in store
(b) he requisitioned extra food from the civilians, which added a further 10%, but also reduced the Local Support rating by 1 [LS is a measure of the citizens' loyalty to the garrison]
(c) he ordered the slaughtering of all the horses in the town (except his own, naturally), which added 3 turns to the food store, but reduced LS by another 1.
There were things he could do beyond these measures, but the LS was now down to -1, which is getting close to open rebellion in the town; it only required another bad Event Card, or a heavy bombardment of mortar shells, and the citizens might just open the gates to the enemy. He already had a situation where one quarter of his available infantry was required to police the townsfolk. So he was running out of food, the enemy were battering his walls, he was in danger of being overthrown by the citizens and the morale score was not great, but we'll get to that.