I’ve always wondered why …
Department of Health is http://www.doh.gov.uk and not http://www.dh.gov.uk (doh!)
Department of Work and Pensions is http://www.dwp.gov.uk and not http://www.dowp.gov.uk
Department for Transport is http://www.dft.gov.uk and not http://www.dot.gov.uk (dotdotdotgovdotuk!)
and then, in the non-government curious world …
try typing “http://www.hm” in your browser, as I just did (trying to get to hmcustoms and getting ahead of myself).