Government inspectors have begun checking up on companies to make sure that they have banned the use of plastic cups for water and coffee and are using proper cups and mugs instead.

Since January 1 this year, “closed locations” such as offices, sports clubs and schools have been required by law to replace plastic cups by sustainable alternatives.

The move is part of a string of initiatives to cut the use of single-use plastics by 40% over two years.

Inspector Gert van Rootselaar told broadcaster NOS he was “pleasantly surprised” by what he had found. “A very large number of the companies we have visited had already switched to sustainable alternatives last year,” he said. “Many turned the change into something fun, such as a price for the most original mug.”

Most companies have gone for glass or earthenware cups and mugs. “We see all sorts, such as personalised mugs but there are also companies who emptied a shelf at IKEA,” he said.

However, two unidentified companies, both employing hundreds of people, failed the test, Rootselaar said.

Rootselaar encountered “shocked faces” when he revealed the purpose of his visit at one of the two firms.

During the inspection the person who accompanied him happened to receive a phone call saying plastic cups would be phased out by Christmas. “I will of course be back in January,” Rootselaar said.

If he finds plastic cups again the warning will be followed by a fine, he said.