Former Shell chief joins attacks on Government tax relief cap The City grandee Sir Mark Moody-Stuart has joined the argument over the Government's plans to cap tax relief on charitable donations. He warned the so-called charity tax will hit current donation levels. "A cap will have an impact on donor behaviour," Sir Mark wrote in an open letter. The 71-year-old was chairman of Shell until 2001 and serves on the boards of several charities, donating between 13 and 44 per cent of his annual income to charitable causes. "We have been considering making some larger capital gifts to allow institutions to build endowments to fund some regular donations," he said. But the proposals forced him to change plans. "The institutions will have to wait until my wife and I are dead or we get a more charity-minded Chancellor," he warned in the letter published in the Financial Times. Sir Mark last challenged the Government in 2008, calling for a ban on "gas guzzlers" and a move to energy-efficient vehicles.