There isn't a direct answer to that, but we do know that Greater London is about 14 million passenger journeys at Gatwick, about 40 per cent of the total.What is rail's modal share between London and Gatwick?
The South East region is about the same, leaving about 7 million from further away. Most of the South East total is Kent, Surrey, East Sussex and West Sussex, which are all 2.5-2.7m each.
For Gatwick coaches are only 5%, much lower than Luton (21%) or Stansted (18%).Most of the rest is likely coaches, which are also public transport.
Coach travel looks like a good way to expand the public transport share at Gatwick.
As the airport expands, rail has to capture the same or higher share of the new London traffic, by expanding rail capacity. If that doesn't happen the rail share will be going backwards.But rail is highly likely to already have a massive percentage of the London/Croydon to Gatwick market.