Disgraced former health secretary Michael Matheson is coming under pressure to "do the right thing" and quit as an MSP after Parliament's corporate body found he breached Holyrood's code of conduct.

Following a lengthy investigation, the Scottish Parliamentary Corporate Body (SPCB) said they had upheld three complaints about the ex-minister relating to his £11,000 iPad data roaming bill.

The SPCB has now referred him to the Scottish Parliament's Standards, Procedures and Public Appointments Committee which will decide if he should face any sanctions, including possible suspension.

READ MORE: Yousaf praises Matheson's 'notable achievements'

Opposition parties rounded on the First Minister, who robustly defended his colleague, even defending him as a "man of integrity and honesty."

Labour said Humza Yousaf had been "complicit" in Mr Matheson's attempts to mislead parliament. 

In a statement, the SPCB said the evidence led them to find that Mr Matheson had breached section 7.4 of the code of conduct.

That states that "no improper use should be made of any payment or allowance made to members for public purposes".

Mr Matheson was also found to have breached section 7.3 which states that MSPs must abide by the rules. 

The body added: “While the costs to the public purse had been addressed, the SPCB agreed that the Nolan Principles of Standards in Public Life, embedded in the Scheme and underpinning the appropriate use of parliamentary resources, represented the high standard by which all members must abide and in which the SPCB considered the public must continue to have confidence.”

The SPCB said they would not release their report into the SNP MSP until the standards committee has completed its consideration.   

READ MORE: Michael Matheson 'lied flat out to the Presiding Officer'

The initial findings of the investigation by the SPCB were passed on to Mr Matheson on February 8, just hours after his resignation. 

He had two weeks to respond but asked for and was given an extension which ended on March 3. It is not clear why it has taken another 11 days for the findings of the investigation to be published.

Mr Matheson came under scrutiny last November when the Daily Telegraph uncovered a £10,935.74 data roaming bill.

He initially agreed to pay £3,000 from his taxpayer-funded expenses, with the Scottish Parliament picking up the rest. 

However, days later, after journalists and MSPs queried the charge, he agreed to pay the full amount from his own pocket. 

At first, he claimed the bill was the result of parliamentary work and a misunderstanding with a new sim card.

He then told MSPs that he had just discovered his boys had been watching football during the family trip.

He said he had been told by his wife that the teenagers had used his parliamentary device as a wifi hotspot.

Mr Matheson then referred himself to the SPCB "to consider whether they think the matter needs to be investigated further."

Reports in the Sunday Mail later claimed that Mr Matheson had misled Holyrood’s Presiding Officer. 

The paper says he told Alison Johnstone he did not know why his bill was so high even after he had learned that his children had used the device.

It’s understood Mr Matheson met with Ms Johnstone after he learned about his sons' use of his parliamentary iPad on 9 November and before his personal statement to the Parliament on 16 November.

He has already admitted lying to journalists. When he was asked on 13 November if there was "any personal use" of the device during the family holiday, he told reporters: "No”.

When asked if anyone else could have used the device, he, again, said, "No".

Mr Yousaf later said Mr Matheson's lie was because he was trying to "protect his children from media scrutiny and media spotlight."

Mr Matheson has not been seen in Holyrood since resigning.

Like all those leaving office, he is automatically entitled to a one-off tax-free payment equal to 25% of his final salary, which, in the ex-health secretary's case, will be worth £12,712.25

Scottish Labour Deputy Leader Jackie Baillie said “The conclusion of this long running investigation is to be welcomed – but the findings pose serious questions for the First Minister and the SNP government.

“The fact is that Humza Yousaf and senior ministers were complicit in Michael Matheson’s attempt to mislead the parliament.

“This is a serious error of judgement. Appropriate action must be taken against Mr Matheson.”

READ MORE: Neil Gray: Michael Matheson has a 'right' to his £13k 'golden goodbye'

Scottish Conservative Chairman Craig Hoy said: “This is a devastating and damning report for the disgraced former health secretary.

“It is little wonder he was shamefully stalling for time on its publication given he has been found to have breached the MSPs’ code of conduct multiple times.

“This amounts to the most serious of charges against any elected member and Mr Matheson must do the right thing and resign as an MSP now. 

“He must also confirm that he will not take a penny of his ministerial severance pay given what the report has found.

“The public saw through the repeated lies from the outset and now they have been fully exposed. Humza Yousaf also must urgently explain why he backed his former Cabinet colleague for so long, rather than sacking him when his lies were first uncovered.”

Scottish Liberal Democrat leader Alex Cole-Hamilton said: “From the very start, the First Minister insisted that the public had no interest in this affair and that there was no case to answer. Now, Michael Matheson has been found to have breached the Code of Conduct for MSPs on two separate grounds.

“At best the First Minister was extremely gullible about the conduct of his former Health Secretary, at worst he was complicit in covering it up.  “It is vital that we now let the Standards Committee do its work and consider an appropriate sanction.”

A spokesperson for Mr Matheson said: "It would not be appropriate to comment while the matter is being considered by the Standards committee."