Which? has 680,000 magazine subscriber members, and over 335,000 online subscribers. It said it had surveyed over 5,500 of its members in June, of whom 2,500 had upgraded to Windows 10. It found that 12 percent of upgraders had rolled back to an earlier version of Windows.
The group said some respondents had paid technicians to repair problems that appeared after the Windows 10 upgrade, which in some cases took place despite users declining Microsoft's upgrade notifications. Which? members complained of being "nagged" by Microsoft alerts to install the update.
"Which? is shining a light on the problem and calling on Microsoft to improve its customer service and repair and compensate its customers where appropriate," it said.
Microsoft said: "The Windows 10 upgrade is a choice designed to help people take advantage of the most secure, and most productive version of Windows. With more than 350 million monthly active devices now running Windows 10, the vast majority of customers who have upgraded to Windows 10 over the past year have had a seamless, positive experience. That said, for the relatively small number of users who may have issues with their upgrade experience, Microsoft offers a variety of options to get assistance including free customer support."
Of course, the Windows 10 upgrade is now over but the Which? survey and call for compensation add to a steady stream of complaints about Microsoft's handling of its one-year free offer to Windows 7 and Windows 8.1 users that began last July. Today it costs $119 to upgrade to Windows 10.
The UK consumer group's call also follows US online rights group the Electronic Frontier Foundation in August blasting Microsoft for "disregarding user choice" during its one-year upgrade program, which "went from annoying to downright malicious".