Since the two new climbing lanes opened on Monday there has been confusion as startled drivers struggle to adjust to the new design which is supposed to make the road safer and less congested.

Drivers are being caught out as the outside, fourth lane is phased out, causing sharp braking and near misses.

Gemma Tait, 25, of Shelford Road, Milton, Portsmouth, said: 'The new layout seems to be causing more harm than good.

'No one seems to know what they're doing.

'When the fast lane disappears it just seems to go to pot. You've got people braking like hell to get in the third lane, or panicking and dangerously cutting people up.'

Jenn Davies-Parker, 45, of Binsteed Road, Buckland, Portsmouth, said: 'People are slamming on their brakes to move over, and then you have people in lane three being stubborn and not letting them in.

'It just seems a nightmare, they should have left it alone.'

Some motorists believe the Highways Agency has made a mistake in its work.

Jerry Clark, of Invergordon Avenue, Cosham, said: 'No wonder we have such bad congestion when the roads department seem to have no idea what they are doing.'

But other drivers say the blame lies with other motorists, not the road layout.

Andy Hawthorn, 27, of The Spring, Denmead, said: 'You can't blame the road layout.

'It's not a one-off design, they have it on the M25, the M3, the M1. People cope there, but it seems that drivers here just aren't looking at the new signs.

'It's the motorists not reading the road causing the problem.'

Roger Jones, from the Highways Agency, defended the road layout.

'The climbing lanes on the M27 have been designed in accordance with the Highways Agency standards for design.

'Drivers have three sets of warning signs, 800 yards, 400 yards and 200 yards in advance of the end of the climbing lane.

'These signs are in both the verge and the central reserve. In addition there is further information in the form of warning arrows and hatched markings at the end of the lane.'