The man at the centre of the SwissLeaks tax scandal in Britain is a soft-spoken Church of England clergyman who turned HSBC into Europe's biggest bank, and was once seen as a model of ethics in finance.

HSBC's former chief executive and chairman, Stephen Green, used to be courted for his advice by politicians of all stripes and by the Anglican hierarchy, but now he finds himself widely shunned.

The ex-banking titan was pursued down a London street by a BBC journalist this week in the wake of the revelations, refusing to answer questions.

"I'm not prepared to make any comments about HSBC business past or present," the 66-year-old Green said before walking off, clutching his briefcase.

Growing pressure may force him to change his mind.

Green has been asked to testify before a British parliamentary committee which is investigating who knew what, when about alleged tax dodging strategies on accounts containing tens of billions of pounds.

The fall from grace has been particularly astonishing for a man praised for steering HSBC through the global financial crisis without the bailouts using taxpayer money that other banks resorted to.

The son of a lawyer, Green began his career with the management consultancy McKinsey in 1978 and joined HSBC in 1982, rising to the top of an institution with its historical roots in the British empire.

As he rose through the ranks in his 28-year career with the bank , he was also ordained as an Anglican clergyman in 1988. He has spoken frequently about the need for an ethical approach in banking.

He has written a book entitled "Serving God? Serving Mammon?" about how to reconcile being a Christian with working in finance, as well as calling for "enlightened" capitalism.

The links between the Church of England and the world of business are not so unusual and there are many ordained clergy in secular employment.

Since his retirement, Green has also advised the Church of England on how to reform its hierarchy -- putting forward proposals that have proved controversial as being too business-minded.

In a letter in the Guardian this week, a fellow clergyman, Reverend Paul Nicolson from the campaign group Taxpayers Against Poverty, criticised Green.

"The Rev Stephen Green's chairmanship of HSBC while legal tax avoidance and illegal tax evasion were taking place raises important questions for the Church of England about the role of all clergy in secular employment," Nicolson wrote.

The focus of the political controversy over Green, however, has been his time in government in a period after the revelations about HSBC's Swiss private banking arm first surfaced in 2007.