By Alistair Smout LONDON, June 8 (Reuters) - More than a third of lawmakers from Britain's governing Labour Party signed a letter on Monday calling on the British government to end trade with Israeli settlements in the occupied West Bank. Prime Minister Keir Starmer has had to balance Britain's historic position as a close ally of Israel and the United States with pressure from within his centre-left party to take a firmer line over Israeli actions towards Palestinians.