Soaring bonuses may have made private jets the carrier of choice for the City’s millionaire commuters, but in the privacy of their Learjets many are beginning to question the cost to the environment.

Air Partner, a listed air charter company whose customers include royalty, heads of state and pop stars, has launched a scheme to cater for climate-conscious travellers, allowing them to offset their carbon emissions whenever they fly. These “carbon neutral” flights are the first to be offered as an option by a private aviation company.

For customers who buy Air Partner’s JetCard, essentially a travel pass for frequent flyers, the flight would cost just under £5,000 an hour. The aircraft itself, an eight-seat Cessna Citation XLS, costs £6 million, but those who want to buy one will have to wait until 2009.

“This is like buying a Ferrari or a Rolls-Royce,” Jonathan Breeze, managing director of JetCard, said. “They’re built to order. It doesn’t matter who you are or what money you’ve got. You have to join the queue.” Air Partner’s clients do not lack the cash. “A typical JetCard customer would have a net worth of about £5 million and would have an income of about £1 million a year,” Mr Breeze said.

These customers have become increasingly concerned about the carbon footprint generated by their flights, he said, prompting Air Partner to roll out a Carbon Neutral JetCard, which costs 2 per cent more than the regular card.

To fly on a midsize aircraft such as the Citation XLS, cardholders would normally have to pay £120,000 for 25 hours of flying time. However, a flight that returns the same day would get a 15 per cent discount.

“We’ve spoken to current and potential customers. What surprised me was the number per cent to 30 per cent who asked about the footprint of their likely jet activity,” Mr Breeze said. “I thought we would need to push this to them. In some respects, it’s been the other way round.”

Air Partner runs the scheme in partnership with The CarbonNeutral Company, a climate change consultancy, and the Edinburgh Centre for Carbon Management. Jonathan Shopley, chief executive of The CarbonNeutral Company, said that air charter companies were starting to catch up with scheduled airlines, such as British Airways, which allows customers to offset their carbon emissions by making a donation when they pay for their flights. He said that he was in talks with four other private aviation companies that are considering a CarbonNeutral scheme.

“The issue of climate change has arrived in the aviation sector,” he said. “Every company is thinking about what they are going to do about it.”

According to the European Business Aviation Association, (EBAA) business flights, including those by private jets, represent 6 per cent of air traffic on the Continent but less than 1 per cent of emissions. However, business jet flights are set to grow. They were up almost 9 per cent in 2005 and the EBAA predicts an extra 1,100 flights per day by 2015.

Friends of the Earth called this “a worrying trend” and said that it had concerns about offsetting. “It’s a way of putting off the inevitable and not looking at how we change our behaviour,” Richard Dyer, the group’s aviation campaigner, said.