A French user, Penny Powell, posted images to Facebook last month showing what looks like a build up of mould in the two-piece valve.

This part of the bottle cannot be opened to be cleaned and, under certain conditions can lead to a build up dirt and possibly bacteria.

Since the issue was reported, Tommee Tippee have been quick to respond with a statement in which they sincerely apologised to any parents who have been affected by the mould issue.

"The company will be launching a new Sippee cup in the next few months, which will have a two piece valve that can be used with different types of liquid and is easier to clean.

The statement added: "In the meantime, we are making transparent, see-through valves immediately available to any parents that have concerns.

"The see-through valve will enable parents to see inside and give them confidence that the valve is clean, when used in line with recommended instructions.

"If you would like to receive a see-through valve or alternative cup please contact our Careline on free phone 0808 206 8000, and one will be sent as quickly as possible.