Vassall, a civil servant working in the Admiralty, had been revealed the previous year to be a Soviet spy, and considerable criticism had been levelled at the security arrangements that were in place.
Before it could begin, letters were discovered in Vassall's possession from Tam Galbraith, who had been Civil Lord of the Admiralty.
Vassall had been Galbraith's junior private secretary, but some people suggested that it was odd that a minister would communicate by post with an official of his own department, and there was considerable speculation of impropriety in the press.
Eventually, the Prime Minister was compelled to open a wider inquiry, conducted by three jurists: the Viscount Radcliffe, Mr Justice Barry, and Milner Holland QC.
The inquiry was controversial in some quarters for requiring journalists to reveal the sources that they claimed for their allegations and for having prosecuted two journalists, Brendan Mulholland of the Daily Mail and Reg Foster of the Daily Sketch, who refused and were jailed for contempt of court, Lord Radcliffe[1] sentencing Mulholland for six months and Foster for three months.