Try entering http://hmrc.gov.uk. As this is the website for Her Majesty’s Revenue and Customs, one would assume that just entering HMRC without the www would work. After all, it’s a very minor setting for any hosting provider to set up a TLD (Top Level Domain) so that there is no requirement for the wuh-wuh-wuh part of it.
If you are accessing websites through a mobile device, which an increasing number of people do, typing www is a bore. And completely unnecessary as you shouldn’t need the 3 w’s to get to a site.
Any website designer who uses a mish mash of capitals and lower case letters in file names below the TLD (e.g. http://www.fsb.org.uk/accessAbility-intro) should be shot as it invariably leads to a 404 error and often a lost punter or conversion, particularly when the website address has been communicated verbally, but in the TLD, neither capitals nor WWW should matter.
Check your site today. You could be losing visitors unnecessarily if you don’t regularly review this much-forgotten aspect of web usability best practice.