BBC Scotland examines the Murray Group Remuneration Trust scheme.
What is an Employee Benefit Trust?
A trust enables an individual to own an asset on behalf of someone else. The first person is the "trustee" and the second is the "beneficiary". Company pension schemes are a common example of a trust.
With EBTs, the employer deposits money in to the trust, which is paid out to the beneficiaries in the form of tax-free loans.
Trusts are often postponed and are sometimes refused by the trustee, who is, in theory, acting independently of the employer.
In many cases, the loans are never repaid.
Why are Rangers in a court dispute with HMRC over EBTs?
Payments from an EBT should not be made on a contractual basis, as it would make them part of an employee's salary and subject to tax and National Insurance.
HMRC claims that Rangers' EBT scheme was a tax scam as it was contractual, which forms the basis of the so-called "Big Tax Case".
HMRC also insists it has proof of this in the form of documents and emails between former directors at Rangers and players' agents.
In 2010, HMRC issued Rangers with a bill for £35m in unpaid tax and interest, and £14m in penalties which Rangers challenged at the Court of Session in Edinburgh, but the verdict has not been announced.
Have any other Scottish football clubs been involved with EBT schemes?
BBC Scotland Investigates wrote to all of the Scottish Premier League's member clubs and asked whether they had ever operated an EBT scheme.
Celtic confirmed that it established one EBT scheme in April 2005, which BBC Scotland understands was for the benefit of the Brazilian midfielder Juninho Paulista. The scheme was worth £765,000 but the club did not declare the trust payment to the Scottish Football Association or the Scottish Premier League.
The payments made to the trust were declared in Celtic's annual report for 2004/2005, but in 2008 the club became aware of an event giving rise to a potential tax liability which was subsequently paid after agreement with HMRC.
The remaining 10 SPL clubs replied and confirmed they had never set up an EBT scheme for any of their employees.
Who set up the EBT scheme for Rangers and the Murray Group?
A former lawyer who advised companies on tax strategy known as Paul Baxendale-Walker. He was struck off the roll of solicitors by a disciplinary tribunal in 2007. Mr Baxendale-Walker is the author of two books on EBT tax strategies and advised Rangers on how to set the scheme up and operate it.
He subsequently became involved in the porn industry, producing, directing and acting in films under the name Paul Chaplin.
How much did Rangers and the Murray Group pay into their EBT schemes?
Between 2001 and 2010, Rangers paid a total of £47.65m in to their Employee Benefit Trust. Details of the amounts paid in to the trust were declared in the club's annual accounts.
Rangers also operated another tax avoidance scheme for two former players, Tore Andre Flo and Ronald De Boer, between 2000-01 and 2002-03 known as a 'Discounted Options Scheme' - commonly referred to as the "Wee Tax Case". HMRC issued Rangers with a bill of about £4m for outstanding amounts owed from the discounted options tax scheme, which was settled, but has not been paid.
BBC Scotland understands the Murray Group paid at least £10m to the trust.
How many beneficiaries were involved the Rangers EBT scheme?
A total of 111 sub-trusts were set up between 2001-2010 for Rangers directors, players and other staff - along with employees of Murray International Holdings and its subsidiary companies.
A total of 53 Rangers players and staff received side contracts giving undertakings to fund their sub-trusts with cash, according to documents seen by BBC Scotland.
How much money did the beneficiaries withdraw in loans from the scheme?
The amounts varied from a total of £6.3m received by Sir David Murray to £7,500 for Bellshill-born defender Steven Smith, who left the club in 2011.
Former Rangers captain Barry Ferguson received a total of £2.5m while ex-Ibrox player/manager Graeme Souness received £30,000 from the scheme almost 10 years after leaving the club.
The average amount received by Rangers and Murray Group employees was about £445,000.
What if Rangers players have received side-letters?
BBC Scotland has also seen evidence, which was submitted to a court, suggesting that 53 Rangers players and staff had side-letters giving undertakings to fund their sub-trusts with cash.
According to the Scottish Football Association's registration rules, payments received by a player solely relating to his playing activities must be fully recorded and declared, otherwise the player has been improperly registered.
If a player is deemed to be improperly registered, the norm is for his team to forfeit any match in which he has participated.
So, could Rangers be stripped of past titles and trophies?
Precedence exists for this kind of rule-breaking and subsequent punishment in football and other sports.
In 1994, Marseilles were found guilty of financial irregularities and a match fixing scandal involving then president Bernard Tapie.
The French club was forcibly relegated to Ligue 1 and lost its 1992-93 Division One title and the right to play in the Champions League in 1993-94, the 1993 European Super Cup and the 1993 Intercontinental Cup.
Rangers: The Men Who Sold the Jerseys was broadcast on BBC One Scotland on Wednesday 23 May, and will be available afterwards for one week on the iPlayer.