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London mayoral candidate Sadiq Khan claimed that using the city's tube service is more expensive than taking a luxury flight to New York City, according to the Evening Standard.

They quote the Khan campaign as saying a 6,904 mile round trip to New York on a Virgin Atlantic first class ticket costs £2,200 ($3,160), which averages out to 32 pence a mile.

Conversely, "a return journey using pay-as-you-go [with an Oyster card] from South Kensington in Zone 1 to Heathrow Terminal 3 in Zone 6 costs £10.10 — 42 pence per mile."

Khan added that some tube journeys come out to as much as 63 pence per mile. A spokesman for Sadiq Khan didn't immediately respond to an emailed request for comment.

Transport has become a big issue in the London mayoral campaign. Khan, a Labour candidate, is running against the Conservative Zac Goldsmith and has promised a "modern and affordable" transport service as part of his manifesto. This will entail four year price freezes and a new one hour bus ticket.

As Business Insider reported on Wednesday, Goldsmith described Khan's promises as 'reckless,' in an outburst many took as a sign that he would continue to raise transport prices if he became mayor.

Last year, Labour's other mayoral candidate Tessa Jowell said that London had the most expensive public transport in the world, with "Londoners are paying more than double the fares of any other city, apart from Washington DC."

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