I saw a segment on BBC News yesterday. Food supplier was challenged as to how he would cope with the end of cheap european labour. Bloke said he was fine with that - as long as it was realised it would also mean an end to cheap food prices
Maybe a more sustainable model might be to turn the vast open (largely unused) spaces of the outside perimeter over to foodstuff stalls from independent vendors. Almost guaranteed to be top-notch on quality. Don't think there's many that would begrudge a reasonable mark-up on price for something...