Scotland may not move to the lowest level of lockdown until September, the country’s national clinical director has warned after disclosing that the Indian or delta variant had pushed back the timetable by up to 10 weeks.

Jason Leitch said "we have lost about eight to 10 weeks on that journey" because one dose of vaccine provides only 30 per cent protection against the new strain, compared to 80 per cent against previous variants.

He said the "horrid" discovery means Scotland will have to wait until all vulnerable groups have received two doses before lifting more restrictions, and some measures will be in place beyond August.

Nicola Sturgeon’s original lockdown timetable would have seen Scotland moving to the lowest Level 0 of her five-tier system on June 28. However, a delay of eight to 10 weeks would mean this being pushed back to between Aug 23 and Sep 6.

All of mainland Scotland was originally scheduled to move from Level 2 to Level 1 of the system earlier this month, but that was postponed for 14 council areas covering nearly all the Central Belt and more than half the population.

The First Minister said she wanted more time to roll out the vaccination programme as the India strain became the country’s most dominant variant. However, she is coming under growing pressure to follow Boris Johnson’s example by setting out a revised timetable for restrictions to be fully eased.

Where is the Indian (Delta) variant in the UK?

Humza Yousaf, the health secretary, said on Sunday he would not "just stick my finger in the air" and disclose for how long the June 28 timetable had slipped.

The number of cases being reported daily in Scotland has surged to more than 1,000, and the proportion of tests  coming back positive has started to edge above the five per cent threshold used by the World Health Organisation to determine whether the pandemic is under control.

However, the number of people in hospital or intensive care has remained extremely low thanks to the success of the vaccination programme.

Prof Leitch told BBC Radio Scotland that distancing, ventilation and handwashing would all still work against the new variant but "the second dose is required for decent protection". 

He said: "This is horrid, and we have learned it increasingly over the last few weeks. You get about 30 per cent protection from one dose, and 80 to 85 per cent protection from two. If you think about this as a timeline, we have lost about eight to 10 weeks on that journey. We have vaccinated about half the adults twice and now we need to get that up.

"At a UK level, a four-week delay gets nine million second doses so that puts it in perspective. If we can just wait another few weeks, the more second doses we can do."

Prof Leitch said the NHS is "trying desperately" to avoid delaying first doses for younger people so that the older and more vulnerable can get their second jab. This is being achieved by giving the Oxford vaccine to the latter group and Pfizer or Moderna to the former.

He added: "If the momentum continues we will be able to do (more) things between now and August, but I don’t think we will be normal by August."