The two ringleaders of Scotland's biggest paedophile ring are expected to be sentenced today.

Convicted sex offender Neil Strachan and gay rights campaigner James Rennie will appear before a judge, a month after their sentencing was deferred to allow experts to prepare the far-reaching background reports required to impose a type of life sentence.

Rennie, 38, and Strachan, 40, were found guilty of a string of child pornography and abuse charges in May.

The pair were snared alongside six other men linked through online chat rooms following a major 18-month police investigation. The others have already been jailed for a total of 43 years.

Rennie had been chief executive of a sexual advice centre for teenagers until his sordid double life was exposed.

A jury found him guilty of offering to let friends abuse a baby boy he was looking after.

Strachan sent Rennie a photo of himself abusing another youngster who was only 18-months old.

The pair, both from Edinburgh, were also found guilty of a catalogue of child porn offences as well as conspiring to abuse children.

Their sentencing was deferred until now because judge Lord Bannatyne said he was considering a form of life sentence for both men.

Such sentences - known as Orders for Lifelong Restriction - require thorough and detailed background reports before a judge can impose them.

A ten week trial, which ended in May this year, heard how a computer hard drive linked to Strachan was sent for repair and found to contain indecent pictures of young boys.

Computer experts also revealed that Strachan had sent a photo of himself having sex with an 18-month-old boy to Rennie.

Police said Rennie sent out sick e-mails offering access to a little boy he had been baby-sitting since the tot was only three months old, and regularly abused the youngster himself.

In total, nearly 125,000 indecent images were seized during Operation Algebra.

The other men involved were sentenced in June, with Glasgow civil servant John Milligan receiving the longest jail sentence of 17 years.

Insurance worker Craig Boath from Dundee was jailed for nine years and nine months, while bank teller Ross Webber from North Berwick was jailed for eight years and nine months.

All three were convicted of plotting to participate in the sexual abuse of children, as well as child porn charges.

IT worker Colin Slaven from Edinburgh was jailed for three years for his involvment in the ring.

Glasgow cake firm manager Neil Campbell was ordered to spend three years and four months behind bars, while sauna receptionist John Murphy, also from Glasgow was jailed for two years.