Registering 17st 4lb (110kg) on the scales, the German Environment Minister, Sigmar Gabriel, ranks - quite literally - as a political heavyweight. Still, it was unusual even for such a generously girthed politician to call in a government Challenger jet all for himself to whisk him from a holiday in Majorca to a Cabinet session in Berlin.

Carbon emission for the trip? About 44 tonnes.

The fact is that Mr Gabriel, tipped by some to succeed the unpopular Kurt Beck as leader of the Social Democrats, is not shy of demonstrating his personal commitment to saving the planet. He was quick, for example, to pose with Knut, the celebrity polar bear cub, and to become his patron. Mr Gabriel sponsors the bear's zoo fodder, an increasingly costly commitment, since Knut is now more hefty than his sponsor.

Now, suddenly, Mr Gabriel, 48, the golden boy of German politics, is under scrutiny. How much are the travels of the Environment Minister damaging the environment?

The Majorca flight is only the latest slip-up. According to the minister, he was summoned by the Chancellery to attend a Cabinet session in August 2007. There were, he said, no available commercial flights, so he ordered an aircraft from the government taxi service based in Cologne. After the short Cabinet meeting he dealt with some files, visited his mother and took a government flight back to his rented villa.

Mr Gabriel is furious that the flights are being held against him. “This is the last time I interrupt my holiday for work!” he fumed yesterday. But it turns out that Mr Gabriel is a frequent user of the fuel-guzzling government flights. Between January and April 2007 he took a Challenger seven times, either travelling alone or with a single member of staff. The newspapers are already calling the flights “Gabriel Wings” or “Air Gabriel”.

Mr Gabriel also heads the list of government ministers who use chauffeured cars, clocking up 55,000 miles (88,000km) last year. “We well remember his supposedly environmentally friendly trip to a place in Germany far away from Berlin,” said the conservative commentator Jochim Stoltenberg yesterday. “Sadly, it did not improve the global ecological balance because he sent his car in advance. Gabriel likes his comforts.”

Mr Gabriel has also argued against imposing a 130km/h (81mph) speed limit on motorways, a highly unpopular move in Germany, which is wedded to fast cars, saying that it missed the point as long as 1.3 billion Chinese were driving vehicles. The key is, he says, “new fuels, new engines”.

In part, Mr Gabriel has been influenced by his political constituency. He comes from Lower Saxony, where, at the age of 39 he was Germany's youngest state prime minister. It is the region where the huge Volkswagen factories are based. He is a protégé of Gerhard Schröder, the former Chancellor, and was once Mr Schröder's plenipotentiary for young people.

This earned him the nickname of Siggy Pop. Since then he has tried to establish more solid credentials and, with Mr Beck enjoying only 13 per cent approval ratings as the Social Democrats' leader, he seemed to be in the running for even higher office.But the Germans, under increasing government pressure to meet ambitious saving targets, are suspicious of ministers perceived to have double standards.

Mr Gabriel gives his hobbies as cycling and sailing. He could do worse for his political image than dig the bike out of the cellar and give his chauffeur - and pilot - the day off.

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