More than 150 Scots soldiers have been embedded with Iraqi forces inside Basra to stiffen wavering government units which last week saw 1000 of their troops refusing to fight fellow Shias and another 400 desert to the opposing Mehdi Army militia, The Herald can reveal.

The Jocks, drawn mainly from the 1st battalion, Royal Scots Borderers, have been split into six "mentoring and advisory" teams equipped with Mastiff and Warrior armoured vehicles for their own protection and dedicated medical support.

They are living alongside Iraqi forces inside Basra city for the first time since the UK pulled back its garrison to a heavily fortified base at the city's airport last September.

The Scots are now set to be on the front line of any renewal of fighting when Iraqi Prime Minister Nouri al Maliki's ultimatum for militia to surrender their heavy weapons expires tomorrow.

The militia, known to British soldiers as the Jam (Jaish al Mehdi), last week agreed to a ceasefire after six days of battles which killed or wounded up to 400 people, but refused to submit to demands for a handover of arms or further arrests of their local leaders.

Mr al Maliki was left politically damaged after he flew south to Iraq's second city to oversee personally the first major test of his government's forces to operate independently against armed militias.

He also ordered two battalions of northern troops south to spearhead the push into slum areas dominated by the Mehdi Army, deploying almost 30,000 soldiers and policemen in total against some 8000 militia.

The lightly armed militia used their local knowledge of the slum areas to dominate the maze of narrow alleys and beat off every attempt to penetrate their strongholds. To add to the Iraqi leader's embarrassment, 1000 Iraqi Shi'ite infantry trained by the US or British armies simply refused to fight against their co-religionists and up to 400 policemen and soldiers deserted to the militia.

The "offensive", which President George W Bush hailed as a mark of Iraqi military progress, ended in stalemate and a ceasefire allegedly brokered by Iran.

Units of the Iraqi 14th Division were left in control of the city centre, while the militia retained their hold through most of the rest of the area and even paraded captured vehicles and members of the security forces they claimed had gone over to their side.

At the height of the battles, British artillery at the airport base destroyed a militia mortar position and RAF and US jets carried out limited airstrikes.

The upsurge in violence was the main reason behind Britain's announcement last week that the 4100-strong UK garrison would not now be reduced by 1600 men and women this spring, as promised by Prime Minister Gordon Brown late last year. Military sources now say there is little chance of a drawdown of troops needed for Afghanistan in the next 12 months.

An MoD spokesman said: "We have been providing key logistical, medical and niche capability support to the Iraqi army. This has included fast air, artillery and the provision of liaison officers at Iraqi headquarter locations within Basra. This has been on top of the training and mentoring we have been providing. In the past few days and alongside coalition allies, we have also started to embed small mentoring and advisory teams within Iraqi army units.

"This is a logical extension of our training role that will provide additional mentoring and monitoring to the Iraqi army, allowing them a greater ability to plan and execute their own operations with their own forces."