The terrific accidental wheeze which means that, as 'non-essential retail' (argue that one, philosophers) commercial art galleries were able to open on April 12 was a boon to those of us who have sorely missed strolling round white spaces looking at things we don't quite understand and are mildly terrified to find out the price of. Now though, we couldn't be more impatient to get into the capital's incredible institutions to revisit old favourites and catch new, long-awaited major shows. Here are the exhibitions to catch once they open in May.