A leading lawyer has warned the families of those killed and injured in the Glasgow bin lorry tragedy face years of uncertainty before they can find out exactly what caused the accident.

A Fatal Accident Inquiry (FAI) into the crash, which left six pedestrians dead and 10 others injured in Queen Street and George Square before Christmas, would compel witnesses to give evidence in a sheriff court.

Yesterday, as around 800 people gathered at a Glasgow church for the funeral of the last of the victims, teacher Stephenie Tait, 29, Patrick McGuire, a partner in Thompsons Solicitors - Scotland's leading civil litigation firm - voiced concerns that families face a lengthy wait for the full facts to emerge.

Currently FAIs are mandatory only for deaths at work and in custody, or if the Lord Advocate decides it is in the public interest.

Even, then, Mr McGuire said, there are no guarantees of scope of FAIs or whether recommendations would follow.

The lawyer, whose firm represents the families of the Clutha helicopter tragedy, said treatment of families exposed to the system was "bordering on inhumane".

Mr McGuire said delays to any inquiry into the bin lorry incident being launched is "the biggest flaw in the system" as time can make it difficult for witnesses to recall events accurately.

Former Holyrood minister Patricia Ferguson MSP has also criticised FAIs, claiming victims and families continue to be left in the dark.

It comes as it emerged the initial report on the findings will be submitted by Police Scotland to the Crown Office in the last week of this month.

In England and Wales, independently-appointed coroners are tasked following a post-mortem examination with opening inquests in the case of "violent or unnatural" deaths or if the cause is unknown.

Fatalities in police custody or prisons also fall under his or her remit.

The Ministry of Justice requires that they are held "as soon as possible" and normally within six months of the death. Often they are opened and adjourned within days of a person's death.

But in Scotland, FAIs into the 2004 Stockline Disaster, where nine people died and 33 were injured in Glasgow, and the sinking of the Flying Phantom in 2007 on the River Clyde, with the loss of three lives, took several years.

Mr McGuire added: "The system is characterised by delays. We've examples upon examples. During this time the treatment of the families borders on the inhumane. They can't go on with life until they know what happened and how their loved ones suffered.

"Strictly speaking an FAI also only has to seek to establish date, time and cause of death but can look at systems failures and recommendations. You can instantly see how there could be raft of issues which would require answers from issues around the lorry to health-screenings and road layouts.

"Are answers here in the public interest? 100 per cent yes but it's entirely up to the sheriff how broad the inquiry would be."

Even if one is held, Mr McGuire added that time was "the biggest flaw in the system" he said, adding that describing it as "not fit for purpose undervalues how bad it is".

Labour MSP Patricia Ferguson has been pushing for reform of the FAI system. She said: "The Crown Office has become better at keeping in touch with families but it's still not as good as I'd like it to be."

A Crown Office spokesman said: "Any final decision by the Crown Office must wait for all necessary inquiries to be completed and it is of course essential that there is a thorough and complete investigation.

"The Crown will consider the initial report and by the end of February provide further information as to the timescale of further investigations required for any criminal proceedings or FAI.

"Specialist staff will keep the families advised on progress and support them throughout all stages of the investigation and any criminal or FAI proceedings which are held."

Reports at the weekend suggested the 57-year-old lorry driver was unconscious and slumped over the wheel as the tragedy unfolded on December 22. It was also reported he had no previous health problems. Three people, including the man thought to be the driver, remain in hospital.