69 firms in the FTSE 100 did not take any measures to optimise their sites.
UK companies are struggling to keep pace with mobile internet adoption, according to new research carried out by technology firm Incentivated for the Financial Times.
The study found that two-thirds of firms in the FTSE 100 do not have websites which are smartphone friendly.
According to the broadsheet's website, most corporate websites are designed for large computer screens and fast internet connections, and this is despite the fact that half of the population browses the web through smartphones.
Jonathan Bass of Incentivated was quoted by the news site as saying that, "FTSE 100 companies are not mobile-ready and are wasting millions of pounds on internet advertising by sending visitors to websites that do not work as users expect them to."
"The lack of investment and inconsistencies among FTSE business should worry all boardrooms," Bass said. "Companies with a mobile-optimised website generate more revenues and customer engagement."
The study found that 69 firms in the FTSE 100 did not take any measures to optimise their websites for mobiles, and the people who accessed these sites found pages packed with tiny text they had a hard time navigating, while some sites took too long to load.
According to the study, 22 firms had taken some measures to give mobile users better access. Based on Incentivated's criteria, only eight companies scored "moderately well", and only the retailer Marks and Spencer scored high, while Rolls-Royce and International Airlines scored low.
Last year, the UK was found to have one of the highest penetrations of mobile technologies with 58% owning a smartphone, while fewer than 19% owned a tablet.