The UK branch of Mars confirmed the news this week, saying: "You may have noticed that some of our chocolates aren't as widely available in stores as they usually are."
The company apologised and added: "We’ve had a mechanical breakdown at our factory in Slough which means that we aren’t able to make as many treats as we would like.
"For the time being, you may not be able to find Maltesers, Revels and some Galaxy treats including Minstrels, Counters and Galaxy Milk and Ripple. No other treats are affected."
The company went on: “We know it’s not ideal and we hate to disappoint, but please be assured that our engineers in the factory are working around the clock to ensure that we are back up and running to full capacity as soon as possible.”
On Sainsbury's website, some pouches of Maltesers are unavailable. On Tesco's online service standard boxes of the sweets and certain Galaxy products are also not for sale.
Mars declined to comment on when the factory would resume normal operations. The company added that its Easter products would mostly be unaffected.
The food business was recently forced to recall bags of its Revels product after it found that some pouches may contain pieces of metal due to another operational breakdown.
