Dave Hartnett, HMRC's former tax chief at the centre of the so-called tax 'sweetheart deals' with Goldman Sachs and Vodafone, has secured an advisory role with Big Four firm, Deloitte.

The appointment, which was approved by the prime minister, David Cameron, will see the 62-year-old take up the one-day-a-week role 'advising foreign governments and tax administrations'.

However, the government's advisory committee on business appointments, has ensured that Hartnett will not be permitted to engage in any work on 'how UK taxation can be mitigated or avoided' or have any 'involvement in discussions with other fiscal authorities of UK's confidential tax policy where he has been involved in that area of work in HMRC'.

He is also prevented from becoming 'personally involved in lobbying government on behalf of his new employer for two years from his last day of service'.

Hartnett played a leading role in negotiating the 'sweetheart deals' with Goldman Sachs and telecoms giant Vodafone, the latter audited by Deloitte.

A spokesperson for Deloitte said: 'Dave Hartnett will work as a consultant to Deloitte advising foreign governments and tax administrations, primarily in the developing world. He has significant experience in advising such countries on the development of effective tax regimes necessary to ensure their continued economic growth. He will not work with UK companies or with HMRC.'

Deloitte's 2012 annual report shows it earned £663m from its audit business, which includes clients such as Starbucks.

A recent High Court ruling on the Goldman Sachs deal negotiated by Hartnett - which enabled the bank to renegotiate £20m in interest payments - was ruled to be entirely lawful by the judge, but dubbed the incident as 'not a glorious episode in the history of the Revenue'.

Since January 2013, Hartnett has been an adviser to HSBC's new board committee on financial systems vulnerabilities. It provides governance, oversight and policy guidance over HSBC's framework of controls and procedures.