Councillors from Munich's conservative CSU party have called the custom version of Ubuntu used by the city "cumbersome to use" and "of very limited use".

Two influential politicians in a German city that ditched Microsoft in favour of Linux are agitating for a switch back to Windows.

The councillors from Munich's conservative CSU party have called the custom version of Ubuntu installed on their laptops "cumbersome to use" and "of very limited use".

The letter from the two senior members of the city's IT committee asks mayor Dieter Reiter to consider removing the Linux-based OS and to install Windows with Microsoft Office.

The city spent years migrating about 15,000 staff to Limux, a custom-version of Ubuntu, and other open source software - a move the city said had saved it more than €10m ($11m).

These latest complaints follow comments by mayor Reiter last year in which he said open source software is "running behind the proprietary IT vendor's solutions".

In a letter to the mayor, city councillors Otto Seidl and Sabine Pfeiler took issue with laptops bought for politicians last year. Despite being high-specced machines, they say they are unable to use them for simple tasks, such as word processing or making video calls.

"There are no programs for text editing, Skype, Office etc. installed and that prevents normal use," Seidl and Pfeiler argue in their letter.

"These devices have already cost a lot of money to acquire. Many town councillors are using their own private notebooks because of the problems," they claim, adding that "a large number of the devices are going unused".

They suggest the council consider taking steps to "acquire Windows licences together with Office for the notebooks".

The Intel Core i7, SSD-equipped notebooks have the Limux operating system installed, which is a custom version of Kubuntu 12.04 developed by Munich.

While the conservative politicians' complained about the lack of word-processing software in the letter, a spokesman for Munich city council confirmed the open source office suite LibreOffice is installed as standard on the machines.

Skype can also be installed on the OS, although the spokesman said it had not been approved as safe by the council's IT department.

Another complaint from councillors is that "the lack of user permissions makes them of limited use".

If the council were to agree with their complaints it would mean installing Windows and Office on the 62 laptops that have been bought for the councillors.

While Otto Seidl didn't answer a request to explain the issues he has, his complaints about Limux mark something of a departure from his earlier views.

Speaking to German IT publication Heise last year he said he was "an advocate of LiMux" and that Microsoft is "not IT paradise". Seidl, an IT consultant and Unix programmer, also described criticisms of IT at the council by deputy mayor Josef Schmid as being an individual's opinion.

The letter is yet to receive a formal response from mayor Reiter. In spite of complaints from these councillors there have been no public signs of widespread dissatisfaction with Limux. In the past a city spokesman described the level of complaints about Limux throughout the council as nothing unusual - with the most frequently cited issue being incompatibility between the open-source office suite and those used by external organisations.

Last year Reiter commissioned a report into the future IT at the council - including which operating systems and software packages - proprietary and open source - would provide best value for money. The review will start at the end of the year and its findings are expected in the second half of 2016.