Britain's FTSE 100 index is seen opening 6 points higher at 6,478 on Tuesday, according to financial bookmakers. * BARCLAYS: British businesswoman Amanda Staveley's private equity firm told London's High Court on Monday it had received a "substantially worse" deal than Qatar when its syndicate invested billions of pounds in Barclays during the financial crisis in 2008. * SHELL: Royal Dutch Shell PLC said it will restart drilling and begin redeploying some non-essen