Dave Hartnett, former head of HMRC, was in the firing line at the Key Havens tax planning conference last week.

Invited as an after-dinner speaker to address delegates at the conference at New College Oxford, a group of activists, operating under the WeAreTheIntruders moniker, posed as black tie clad guests and gatecrashed the event, presenting Hartnett with an award for services to tax avoidance. Initially the audience reacted positively, but the invaders were quickly ushered out of the venue.

Hartnett, who retired from HMRC in 2012, was under fire in the last year of his tenure following accusations of sweetheart deals on tax with Goldman Sachs, following the revelations of a whistleblower.

The issue was highlighted last year after a whistleblower revealed that HMRC had waived as much as £20m of interest on a £30m tax bill owed by Goldmans on bankers' bonuses. It was also accused of letting Vodafone off as much as £8bn in taxes by accepting a £1.25bn settlement.

Although HMRC was cleared of any wrongdoing by the National Audit Office, it was criticised over the way tax disputes with a number of multinational companies had been settled.

The NAO probe, led by former High Court tax judge, Sir Andrew Park, examined the HMRC's approach in five large un-named tax settlements, two of which are believed to be Goldman Sachs and Vodafone.