Guardian: Tory plans to replace a third runway at Heathrow airport with a high-speed rail line were dealt a blow today after a government adviser warned passenger demand for 180mph train journeys might be too low. Robert Cochrane, an adviser to the Department for Transport on long-distance travel, said Britain could not assume the success of high-speed rail networks in Europe would be replicated here. The UK has a different distribution of population and economic centres compared with countries …