LONDON (Reuters) - British Prime Minister Theresa May is fully focused on tackling extremism, her spokesman said on Thursday, responding to a tweet by U.S. President Donald Trump telling her to focus on  destructive Radical Islamic Terrorism . Asked if May was focused on tackling extremism: her spokesman said:  Yes.    The overwhelming majority of Muslims in this country are law-abiding people who abhor extremism in all its forms. The prime minister has been clear ... that where Islamist extremism does exist it should be tackled head on. We are working hard to do that both at home and internationally and ... with our U.S. partners.  