No you won't find any of the big supermarkets open, I think as part of the concession to allow Sunday opening it was agreed that Easter Sunday would be the one Sunday (apart from xmas) when shops would close.
Nope, I doubt it. It has become law that any retail outlet that is over 3000 metres squared has to close today, so shops such as Tesco, B&Q ect. Other shops that are under 3000 metres squared are allowed to open.
This law has only come into affect this year and the only two days which shops have to close - by law, are Easter Sunday and Christmas Day