The UK’s tax agency will have to answer in court for allegedly letting Goldman Sachs off millions in tax, after a top tax official enjoyed cosy lunches with the global investment firm’s people. Incensed at the apparent conflicts of interest, a volunteer army of tax evasion campaigners – UK Uncut – have argued that the case must be heard by the courts, and judges have now agreed.

British MPs calculate that the UK tax agency (HMRC) has let companies off some £25bn in tax. Worse still, they have accused it of obstructing their parliamentary inquiries and criticised HMRC chief David Hartnett for mishandling tax negotiations with some big companies, as well as failing to explain how deals were done.

But now, thanks to the UK Uncut action, and more than 100,000 Avaaz members who called on David Cameron for full details of the Goldman Sachs case, we can expect more juicy details to emerge. Already David Hartnett has admitted that he did not consult his lawyers properly when he personally negotiated a deal to let Goldman off £10m – the interest owed after the bank had spent years trying to avoid paying national insurance on huge bonuses for their UK staff.

Lawyers acting for UK Uncut are now calling for a mass of tax agency documents to be produced in court. They should reveal much more about the relationship between the tax authority and major private companies. The HMRC boss had hundreds of lunches with big business tax lawyers and advisers before a whistleblower lifted the lid: just what did they talk about? We will soon find out.