Fashion designer Stella McCartney's plan to build a £5 million modernist home in the Scottish Highlands is facing further delays over otters.

A leading otter charity has warned that construction must be 'stopped immediately' if cubs are found.

The charity also said someone must monitor the holts on the land constantly while building work takes place. 

The location, known as Commando Rock, was once a place where elite troops were trained for critical missions during the Second World War.

However the daughter of Beatles legend Sir Paul, has become embroiled in her own war at Commando Rock after dozens of objectors accused the famously pro-green activist of hypocrisy in her approach to the build, which some have labelled an act of environmental vandalism.

More than 60 letters of objection warned it could threaten local wildlife including otters and pine martens.

Now a long-awaited otter survey has been lodged which could potentially clear a major hurdle in Ms McCartney and her husband Alasdhair Willis application to Highland Council for planning permission.

The couple previously hired conservationists in an attempt to prove no otters were living in the surrounding area, however evidence mounted that the mammals were living in the area, leading to the specialist survey which was compiled in November.

The couple are seeking permission to build a sustainable, low-profile house on the Moidart Peninsula.

Ecologist Dr Leon Durbin had previously taken to a canoe to prove otters are threatened by the development, which he has objected to.

Now in a new submission Grace Yoxon of the world-leading Skye-based International Otter Survival Fund, says if it had not been for Dr Durbin the application 'may have been successful which she said could have been 'disastrous' for the resident otters.

She said: 'At that time the otter survey was totally inadequate and had completely failed to identify and record any otter activity e.g. Holts, runs, tracks, etc. How they failed to find this evidence certainly does question their competence in otter surveying,' she wrote.

'It is good to see that a second survey has now been done which does record the abundance of activity at this site.

'It is worrying though that if Dr Leon Durbin had not confirmed this evidence with video proof then the application may have been successful with potentially disastrous consequences for the resident otters there.

'Dr Durbin has given a very full and detailed comment on the application as it stands. I therefore do not need to go into all the aspects he mentions and I would like it noted that I support his comments.'

As part of the plans, if approved, the developers agreed to take a break between May and August with no construction work, to protect the otter's breeding season.

However this plan was not satisfactory to Ms Yoxon, who argued the otters do not have a strict breeding season.

She added: 'The application says they will avoid the otter breeding season, but as Dr Dublin says Eurasian otters (the species in question) do NOT have a breeding season and young are born at any time of the year. 

'We have been recording otter activity for over 40 years which proves this. We have also run an otter hospital caring for nearly 300 otters and cubs have been received in every month of the year.

'It is true that at one time otters in Shetland did show a certain degree of of seasonality but since the Braer disaster in 2003 this is no longer the case.

'Therefore construction at any time can cause disturbance.

'Also a gap of three months between survey and construction work is too long. The gestation of an otter is about three months and so a female may not have young during the survey period but may well have by the time the work begins. A survey with camera traps should be carried out just before the start date.

'Clearly any vibration or noise disturbance could well have a serious negative impact on very young cubs. If the female is scared off at such an early stage the cubs will die.

'Any construction must have someone to oversee the holts in case there are young cubs and work must be stopped immediately if this is found to be the case.

'This construction is in a very sensitive area and as otters and their places of rest (holts) are fully protected by law, careful consideration must be given before allowing the application.'

Permission to build a home at the location was granted 26 years ago and foundations for a four bedroom house have been laid.

The couple say their design is more environmentally sensitive and less visually intrusive than the original plan.

Agents for Mr Willis, in whose name the application is made, also commissioned specialists, including the otter survey.

A licence will also be required from NatureScot, and all works will follow its guidance.

A Highland Council spokesperson said it hopes to bring the application to the south planning applications committee early this year.

Since submitting plans in 2023, Mr Willis and Ms McCartney have faced over 60 public objections - with many coming from outside the local area.

Some objectors have also raised concerns the development will be a holiday home.

Mr Willis has always disputed this, saying: 'We're building a permanent family home.

'This is not a speculative investment or holiday let.

'We want to live here full-time and be part of the community.'

He explained that their connection to Scotland runs deep - from family roots in Gaelic-speaking regions to his wife's childhood memories on the Mull of Kintyre.

The couple married on the Isle of Bute in 2003.