To add to all that good advice, we had a similarly prized apple tree (Pixie, our best keeper, crisp till April) knocked over by a gale. When we had pulled it back upright, in addition to David's angled stake we put in a couple of strong stakes about one and a half metres apart beside it and nailed a strong piece of timber across it, against which the trunk could rest. I think that helped a bit too.
Our tree certainly lost some root, so Trevor's top pruning would be good - I wish I'd taken more off the top of ours, as it hasn't fruited nearly so well in the three years since.