Well, nearly. The US government has set up a website that displays a real-time clock that is linked to an extremely accurate atomic clock. The time displayed is accurate within limitations stated on the site - there is a slight error in the display owing to the small amount of time it takes for information to be sent over the Internet. It also includes a nifty World map that shows which areas are in daylight and which are in darkness. However, as it stands, it only shows the correct time for US timezones, though it can also display Universal Time.
Unfortunately, they have seen fit to modify timezone.cgi (the 'active ingredient') during 2007 such that it will now only work with US timezone names (or UTC) as the 'zone name' argument. This has considerably reduced its usefulness outside the US, but for those within the GMT timezone, which includes the UK when not in 'Summer Time', it gives the correct time when UTC has been selected. The JavaScript I wrote in 2005/6, which made it display properly for other (non-US) timezones, therefore no longer works - it just gives an error message.
I regret that I can no longer give you a clock that displays properly for all timezones, but I provide the following links that will give a display in UTC (which is essentially the same as GMT) - this is probably more useful for European users.
Click here for the
time in UTC, or
here
for an alternative site
operated by NIST (the [US] National Institute of Standards and Technology).
I have commented out my original JavaScript so it is inactive, but you may still view the source.