A post-mortem examination found he had succumbed to the effects of carbon monoxide poisoning, although it could not be established whether his death was accidental or deliberate.
In a report published yesterday, the Police Investigations and Review Commissioner (Pirc) said there had been failings in the way Police Scotland responded to reports of concern from members of the public about Mr Penman’s vehicle.
The calls were taken by the control room at Bilston Glen, Midlothian, which was the subject of a major review following the deaths of Lamara Bell and John Yuill in July 2015.
The control room received a call about Mr Penman’s vehicle two days before his body was found.
A local resident who thought the van had been stolen said it had been parked in Old Northfield Road for three days.
But after a computer check established the vehicle was not stolen, a police officer in the control room decided officers were not required to attend and “closed” the incident.
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Another member of the public called the control room on Wednesday 14 December reporting similar concerns about the vehicle, but the report was linked to the previous incident and no further action was taken.
In her report, commissioner Kate Frame said officers should have been sent following each call.
It was only when a third call was made at 7am on Thursday 15 December about another vehicle – an HGV with foreign number plates – that officers were sent to investigate at about 11am.
They were unable to find that vehicle, but found Mr Penman’s van at about 11.50am and saw his body in the driver’s seat.
The Pirc said there were clear inconsistencies in how the police control room dealt with the three calls.
Ms Frame said: “It would be unrealistic to expect the police to investigate each report of an abandoned vehicle.
“However, in this case had the repeated concerns expressed by members of the public been acted on earlier, additional information would have been available which may have prompted officers to locate and search the van in the lay-by sooner.
“While it cannot be determined that if police had acted when the deceased’s vehicle was first reported, he would have been found alive, there are important lessons to be learned in how police deal with similar incidents.”
Mr Penman’s family said they would never know if an earlier police intervention would have saved his life.
In a statement issued through the Pirc, they said: “David was a loving father, son and brother and it has been very difficult for our family to come to terms with his death.
“We are aware of the Pirc report and its findings and we feel that it has provided us with some of the answers we were looking for.
“We will never know for sure whether David would still be alive if more prompt action had been taken initially but we are pleased to note the recommendations in the report. We hope that Police Scotland will take these recommendations on board and that valuable lessons have been learned.”
HM Inspectorate of Constabulary carried out a review into Bilston Glen following the deaths of Mr Yuill and Ms Bell in 2015. Police took three days to find the couple’s vehicle at the side of the M9 after an initial call from a member of the public was not properly logged at the Midlothian control room.
In July, fresh concerns were raised about Bilston Glen following a Pirc report into the death of vulnerable Edinburgh man Andrew Bow.
The 36-year-old’s body was found at his flat in March 2016. Officers were not sent to his home on four occasions when concerns were raised.
Commenting on the latest case, Scottish Conservative shadow justice secretary Liam Kerr said: “This is an appalling case which is frighteningly similar to the M9 tragedy.
“I know the Area Control Centre staff have been working hard to learn lessons since the SNP government mandated centralisation of control centres, but one tragedy is one too many.
“The leadership of Police Scotland needs to spend less time fighting with itself and more time giving support to hardworking officers and ACR staff who just want to get on with the job.
“This incident yet again calls into question the level of planning by the Scottish Government when it made the decision to close call handling centres across the country.
“It is yet another incident on the Justice Secretary’s watch and sooner or later he’ll have to step up and take responsibility.”
Assistant Chief Constable Nelson Telfer said: “Our thoughts remain with the family of Mr Penman and all those affected by his death.
“Following an internal review of this incident, discussions have taken place with Local Policing, C3 Division and Professional Standards and updated guidance has been issued to call handlers and area control room staff to ensure appropriate actions are taken when dealing with a report of an abandoned vehicle.”
A Scottish Government spokesman said: “Police Scotland have made clear they will carefully consider the findings of the Police Investigations and Review Commissioner investigation, taking further action where necessary.”