The Foreign and Commonwealth Office (FCO), which manages the government's official wine stocks, has again refused to make a full disclosure of the cellar's contents in the interests of the taxpayer.

Labour MP Tom Watson has challenged the government to reveal the complete database of its £864,000 wine stock, which is believed to include a number of first growths such as chateaux Mouton-Rothschild, Latour and Margaux.

"This is simply extortionate. People have a right to know precisely what wine is held in the cellar and how public funds are being spent," commented Mr Watson.

The FCO responded that preparations for the impending visit of the pope meant that it was "most unlikely" that the MP would receive a response before the end of August.

It is not the first time the governmental wine cellar has been probed - in 2008, a wag named Alex Skene began a lengthy correspondence in which he requested full details of the number of bottles held, price paid per bottle and "tasting notes".