Mobile web users are being badly let down by some European content providers, a website performance report has claimed.

According to the inaugural Mobile Performance Index from industry analyst Keynote Competitive Research, download speeds to a simulated Nokia N70 phone were up to three times faster from some sites than others, while one site in particular - Eurosports - failed to fully download its content in almost half the tests.

Response times among the ten popular sites selected for the initial survey were uniformly long, varying from 7.42 seconds for Google to download its page to 18.19 seconds for Euronews.

Rather curiously, while the fastest sites to load were Google and Facebook, they came last on download speed. Conversely, Euronews took longest to load but had the fastest download speed while it was loading.

Keynote senior director Manny Gonzalez said that's a function of how content-heavy the different sites were. Lightweight sites lost time to network latency, while rich pages took longer to get going, but once they did, they could fill the pipe with content.

He added that other sites not listed in this index were even more content-heavy, with some downloading over 100kb per page. That might be sound OK when a 3G connection can reach 384kbit/s or more, but if the site is poorly structured or relies on content from multiple servers, the user can still see poor performance.

"Content providers need to recognise that there is a trade-off between functionality and performance," he said. "We're hoping to help people see that lighter sites perform well - though you have to find the right trade-off for you."

Gonzalez said that Keynote will offer a testing service to organisations who want to measure and optimise the performance of their mobile sites across multiple European countries and networks. The company can also help its customers validate their content - it can emulate over 1000 network and device combinations, allowing web developers to test their code remotely.

Also this week, the web consortium W3C announced the first version of its mobileOK fully-automated mobile web content checker.

This runs tests on a site to see if it conforms with best practices for the mobile web, said Dominique Hazaël-Massieux, who leads the W3C's mobile web initiative. "Making a website work on a mobile device is easier once you have the right tool," she added.

Keynote's Gonzalez claimed that his company's testing services did not conflict with mobileOK. He suggested the two could be complementary, with developers using mobileOK to validate their code, then the testing service "to get the full picture."