LONDON (Reuters) - Britain and France are firmly committed to a 2015 Iranian nuclear deal and will work to ensure it is enforced, British Prime Minister Theresa May s office said on Monday after she spoke to French President Macron.  May and Macron discussed U.S. President Donald Trump s decision to not recertify the deal and said that France and Britain would work together to  push back on Iran s destabilizing activity in the region,  May s office said in a statement after the phonecall. 