Next week is Henley Week. Of all the events which use sport as an excuse to ease out the champagne corks and have a social junket-Ascot, Wimbledon, Lord's, Cowes-the most exquisitely English is Henley Royal Regatta. The course is English to the point of idiosyncrasy: it doesn'conform to international standards for one inch of its beautiful length. Yet every oarsman in the world wants to row on it. Even the Russians send their best men to heave and sweat past the Stewards' enclosure, where the English upper classes relax in deck-chairs, wear dazzling boat-club blazers, sip champagne, gossip with pretty women, and clap politely. Jack Pizzey was at Henley last summer, mingling with the crowds and looking behind the scenes of this most English occasion. Producer RICHARD Thomas