As immigration minister Caroline Nokes spoke to reporters in Dover on Saturday, a black Border Force boat sailed purposefully behind her, as the cameras clicked away.

But last night the Home Office faced questions over whether the vessel was really on patrol, or instead part of a “meaningless PR stunt”.

According to onlookers, the boat spent the majority of Ms Nokes’s visit sailing around in circles behind her, with three crew members on board.

One claimed the craft was even performing so-called “donuts”, fast manoeuvres to show off its power and speed.

“It was totally bizarre,” the onlooker said.

“The boat was just going around in circles totally pointlessly, right behind where she standing.

“It was like someone had decided to show the public that the government really had got control of the situation, and that they were dealing with it.

“But it seemed like a total waste of time. Surely the boat should either have been out in the Channel, or saving petrol?

“It just seemed like a charade, a meaningless PR stunt. It was all for show.”

The vessel seen sailing behind Ms Nokes is believed to be a Border Force rigid hull inflatable boat (RHIB).

Nearly eight metres long, the craft does not patrol the seas but instead carries crew from the shore to one of the force’s five cutters.

According to the Home Office website, the vessel is usually “launched down a slipway in the stern of the cutter, allowing for safe and speedy deployment and recovery in most sea conditions”.

It is not clear what task it was performing while sailing behind Ms Nokes on Saturday afternoon.

Only one of the Border Force's fleet of cutters is currently operational in the Dover Strait.

The Home Office was approached for comment, but failed to respond.