FLORENCE, Italy (Reuters) - Prime Minister Theresa May said on Friday that negotiations on Britain s departure from the European Union had been tough at points but made concrete progress.  We have now conducted three rounds of negotiations and while at times those negotiations have been tough it s clear that thanks to the professionalism and diligence of (negotiators) David Davis and Michel Barnier, we have made concrete progress on many important issues,  May said during a major speech on Brexit in Florence.  