Two new environmental campaigners have boarded an oil rig which was being towed out to sea, continuing a protest calling on BP to stop drilling for new wells.

Greenpeace activists pulled up in a boat alongside the rig in the Cromarty Firth, near Inverness, on Sunday evening before climbing aboard and unveiling a banner declaring a climate emergency.

Late on Monday night, the pair who had been protesting for more than 24 hours were relieved by two new activists boarding the rig with fresh supplies.

They are occupying a gantry on a leg of the 27,000-tonne rig below the main deck, hoping to stop the drilling rig from reaching the Vorlich oil field where it is believed to be trying to extract up to 30 million barrels of oil.

Pete, one of the new activists, said: "The UK could make history by becoming the first major economy in the world to set a target to completely end its contribution to climate change by 2050.

"But we will never be able to achieve that goal and tackle the climate emergency if companies like BP are still allowed to send their rigs out to drill for more oil in the midst of a climate emergency.

"If ministers are serious about hitting a net zero greenhouse gas emissions target, they should ban all new oil and gas exploration and stop the industry from draining the last drop of oil out of the North Sea.

"Today, it's us trying to stop the fossil fuel industry from wrecking our children's future. Tomorrow, it should be the government."

Responding to the protest on Monday, a BP spokeswoman said: "In all operations, safety is our top priority. "While we recognise the right for peaceful protest, the actions of this group are irresponsible and may put themselves and others unnecessarily at risk.

"We are working with Transocean - the rig's owner and operator - and the authorities to assess the situation and resolve it peacefully and safely.

"We share the protesters' concerns about the climate. We support the Paris agreement. And we are working every day to advance the world's transition to a low-carbon future.

"We're reducing emissions from our own operations - down 1.7 million tonnes last year - improving our products to help our customers reduce their emissions, and creating new low-carbon businesses.

"We are committed to being part of the solution to the climate challenge facing all of us."