A KEY Scottish road which has been plagued by landslides is shut for a fourth successive day because of heavy rain.

The landslip-plagued A83 at the Rest and Be Thankful in Argyll was shut at 6pm on Sunday ahead of a Yellow weather warning coming into place across much of the Central Belt on Monday morning.

Traffic from the key Highlands route was to be diverted through the single track Old Military Road which runs parallel to the road as a safety precaution.

Maintenance firm BEAR Scotland had confirmed that the iconic A83 will remain shut throughout Tuesday.

Now it has said that it remains closed "as a safety precaution" while geotechnical inspections continue on the hillside.

Western Ferries said it was offering additional sailings to help keep people moving "as quickly and safely as possible".

READ MORE: A83 Rest and be Thankful open just 18 days in over two months shuts yet again for safety reasons

The road has been open for barely three weeks since August 4 when a landslip brought about by rain blocked the A83.

There were further problems last night when the Old Military Road - the single track route which act as a diversion - was shut as a precautionary measure after teams noted heavy volumes of water and silt were overflowing the banks of a watercourse channel nearby.

That left drivers forced to face diversion on other roads of up to 60 miles.

Engineers have since completed a full geotechnical inspection of the slope below the A83 and carried out work to secure the channel, allowing the OMR local diversion route to reopen to traffic.

BEAR Scotland said an estimated 86mm of rain has fallen at the Rest and Be Thankful in the past 48 hours.

Eddie Ross, BEAR Scotland’s north west representative said: “The Old Military Road local diversion route has reopened to traffic after it was closed around midnight last night as a safety precaution.

“Our team identified that one of the channels had experienced a build-up of silt and water after a period of heavy rain, which was causing it to spill across land above the OMR, prompting us to implement a closure for safety.

“The issue has been addressed this morning and the water flow redirected back into the channel as before, allowing us to reopen the OMR.

“We’re continuing with further geotechnical inspections on the hillside above the A83 and paying close attention to weather conditions in the area.

“Safety of all road users is a top priority and we thank all the local community and motorists for their patience while we do everything we can to address the situation at the Rest.”

Ministers have previously been accused of wasting nearly £80 million on more than a decade of failed solutions to landslides on the road after the latest multiple slips in heavy rainfall.

Some locals have called for a public inquiry into the problems, with many saying a permanent solution must be found.

Transport Scotland published details of the 11 "corridor options" for a new route to replace the landslip-prone section of the A83 include building up to three bridges or tunnels.

But the choice of solution is not expected till next year.

The source of the August 4 landslip was located around 200m high above the A83, which split into two main channels as it spread out in a “fan effect” down the hillside.

One of the channels filtered into one of the landslip mitigation catch-pits which prevented around 2,000 tonnes of material from reaching the road, with around 1,500 tonnes of debris reaching the carriageway at the second channel. Car-sized boulders also reached the roadside in the debris. A further 2,000 tonnes of material was washed onto the OMR.

In total, the landslide is thought to have moved around 10,000 tonnes of debris on the hillside following detailed geotechnical calculations of the hillside, making it one of the largest landslips in recent times. Earlier estimates put the original figure at 6,000 tonnes.

On August 6, a further 100 tonnes of material reached the carriageway overnight via the steep channel scoured out by Tuesday’s landslip, exposing large boulders. Teams worked to make these boulders safe using water-bags dropped into position from a helicopter as well as using a high-pressured hydraulic ‘jack’ to force the boulders into a new, safer position further down the steep channel.

Teams completed the clear-up of 2,000 tonnes of debris from the OMR on August 7 and began work to construct a protective bund and channel parallel to the roadside.

The A83 reopened under traffic light control at around 10.25am on September 7. But the A83 and OMR were closed on September 12 due to forecast intense rain. This triggered a landslide which brought over 2,000 tonnes of material to the A83 with some reaching the OMR the following day.

The clearance of the debris started on September 14 as 5,000 tonnes of material had reached the A83 and OMR.