This much is public knowledge: as EU Trade Commissioner, Lord Mandelson received a Montegrappa pen, a carpet, a glass lamp and a gold-inlaid plate, each deemed by the Director of the Office for Infrastructure and Logistics in Brussels to be worth at least €120.

It is also known that Neelie Kroes, the Competition Commissioner, has received a silver fig leaf and a five-volume German-Slovenian dictionary. In total, the 27 EU commissioners have declared that they have received a total of 216 gifts in their four-year term.

The bureaucrats who recorded these items may actually have a sense of humour. Commissioners are powerful and necessarily well connected. It is well known that they are frequent guests on the yachts and jets of the very wealthy. Yet their rules for declaring interests are structured so that any meaningful act of hospitality goes undeclared.

Under the commissioners’ code of conduct, the public cannot know who entertains them or whether they mix business and pleasure in what they choose to call their private time, unless the commissioners themselves choose to say so. Usually, and unsurprisingly, they do not.

The code of conduct was drafted in haste by Neil Kinnock in 1999 after the resignation of Jacques Santer’s entire Cabinet, which had been condemned as shot through with fraud, corruption and bad management. The offences that triggered the upheaval included Édith Cresson’s hiring of her dentist as an adviser on Aids policy even though he knew next to nothing about it.

The code aimed high, and not just by setting the bar low for the value of gifts to be declared. Commissioners were to preserve the dignity of their office “in their official and private lives”, not least by “ruling out all risks of a conflict of interests”. All paid activity unrelated to the EU was proscribed. Even royalties from work-related publications were to be given to charity, and political campaigning was to be cleared with the Commission President in advance.

This was a document that purported to require full disclosure. In practice it leaves commissioners free to disclose nothing at all about whatever they deem to have been private. The Commission’s terse statement that “it is for Mr Mandelson to decide if he wishes to provide the list of his social engagements” is a direct result.

Graham Watson, the Liberal Democrat MEP, was an early and lonely critic of the code. He returned to the attack in 2005, when both Lord Mandelson and José Manuel Barroso, the Commission President, had first been guests on board yachts owned by businessmen with close interests in EU policy. Few took up the cause, which was eclipsed by the defeat of EU referendums in France and the Netherlands. But it remains vital.

Europe’s trade, industry and competition commissioners routinely have the power to help and hurt businesses to the tune of hundreds of millions of euros. They are more influential than all but a handful of national ministers, and their privacy is more closely guarded. Lord Mandelson has argued that part of their roles is to know the business leaders whom their work affects. Perhaps. It would certainly be wrong to cut them off from the worlds in which they operate, but this requires an entirely new level of transparency.

There is a scandal that has been revealed by the events on a yacht off Corfu this summer that both Conservatives and Labour can agree on, namely the shocking laxity of rules governing the gifts and hospitality lavished on commissioners. Lord Mandelson observed them to the letter – and, of course, this was not hard. They are toothless. Mr Barroso must now acknowledge that they give his Cabinet too much freedom to abuse their posts, and he must fix them.