Ever had a sneaking suspicion that your broadband download speeds never quite measured up to the "up to" speeds trumpeted by your ISP—and that everyone around you was probably in the same boat? If so, you now have some solid empirical evidence that this is indeed the case.

UK telecoms regulator Ofcom today released the results of a lengthy study that compared advertised download speeds with the actual speeds received by home users, and the results are shocking—average speeds are only half what is advertised.

Geeks have always understood that the top line speeds promoted by ISPs are rarely going to be seen by a home user, and ISPs are careful to include "up to" language in their advertisements, knowing that actual speeds will be affected by everything from a home's distance from the local exchange, network congestion, Internet congestion, server problems a particular websites, and even issues with old home wiring. Still, they don't typically reveal that people who subscribe to 8Mbps plans have average download speeds of only 4.8Mbps.

That's what Ofcom found when it compared offerings from the UK's eight largest DSL providers. Overall, the average is only 4.1Mbps, and speeds dropped even further in the evening, when home users all go online. Between the hours of 8 PM and 10 PM, average download speeds fell to 3.7Mbps.

When it comes to upload speeds, the situation is just as dire. Average UK upload speeds were a mere 0.43Mbps, not exceeding 0.7Mbps even on 16Mbps plans.

Virgin Media's cable service, which is available to about half the UK, provided better performance than DSL. Its 10Mbps package offered average download speeds that were more than twice as fast as those provided by DSL.

This isn't an academic exercise, one performed for the sheer pleasure of finding things out but having no relevance to the actual concerns of non-geek Internet users. Ofcom's research found that people care about their Internet speeds; speed turned out to be "the single biggest cause of dissatisfaction among those who were dissatisfied" with their service, and 26 percent of all Internet users said that the "speeds they received were not what they expected when they signed up for their broadband service."

This user dissatisfaction is behind Ofcom's push to make ISPs disclose the limitations on speed more effectively. Most major ISPs in the country have signed on to Ofcom's voluntary code of practice, which requires them to make clear to potential customers the reasons why advertised speeds may never be achieved at a particular home. They must also estimate what the actual line speed at a particular address will be.

As for the survey itself, it appears to have been quite robust. Hardware monitoring units were sent to 1610 homes, where each was connected directly to the home's router. Each monitoring unit conducted more than 7000 tests per month, but only did so when it detected no other network activity on the line. Data was collected for the six months from November 2008 to the end of April 2009, and it showed little variation by month.

Low speeds, it seem, know no season.