Weblink broken

I sent an email to one site after mentioning that a link which was coded as <a href="http:\\www.sitename.co.uk"> didn't work. After the initial response of "it works on my pc" I was told that 98% of browser users are Internet Explorer, which accepts the slashes in the wrong direction. Fortunately they changed the link. What they don't understand is that the original code is plain and simply wrong, a basic bit of code that is almost the first thing you learn when coding html - but then again if you code a web page using frontpage........