So once again the issue of a New Thames Estuary airport has been put on the agenda by the Greater London authority.
Dont get me wrong. I recognise completely the importance that aviation links play in the competitiveness of the British economy - and I think that Boris and his team are quite right to highlight the need to plan for and deliver more airport capacity in London and the South East.
But the debate seems to be driven by an ethos of 'anywhere but Heathrow' rather than any objective assessment of where additional capacity should be focused. And conveniently, the Thames Estuary option falls conveniently well away from the Greater London Boundary. It isn't really the place of anyone at City Hall to dictate what happens in North Kent and South Essex.
Let us be clear. A new airport in the Estuary or nearby would pose a number of issues and practical problems.
Firstly, the construction of such an airport would represent a massive engineering challenge and would be very expensive. The billions it would cost would have to come from somewhere. Who will pay? It could not be justified from the public purse, when it would be clearly much cheaper to expand capacity at existing airport facilities. The estimated cost of a new airport in the Estuary is £33bn, as compared with an additional runway at Heathrow which would cost £7bn.
Secondly, it would require major investment in supporting infrastructure to get people to and from the airport. Again we are talking billions of pounds. It would require new rail links, new roads and new tunnels under the Thames to get people there. Again, all additional burden on the taxpayer, when investment in Crossrail is improving links to Heathrow.
Thirdly, this is an idea which has been examined repeatedly over the last fifty years - each time it has been ruled out on the grounds of economic viability and cost.
Fourthly, the environmental impact has not been properly assessed, although the RSPB are fiercely opposed to the scheme due to its impact on bird habitats in the Estuary. At a time when we are seeking to address the impact of climate change we need to understand what the impact would be in terms of traffic emissions and wider environmental consequences.
Fifthly, there are very real safety issues. Wind and fog would cause operational difficulties at such an airport. There is also an increased risk of bird strikes which can pose significant risk to aircraft.
In many ways, Heathrow is a victim of its own success. Heathrow has great advantages - proximity to the capital - good road and rail transport links - all of which have attracted passengers and airlines which have seen it emerge as a highly successful European transport hub and one of the busiest airports in the world. The hub model we see at Heathrow is one which informs airport investment across Europe and indeed the suggestion of a new hub in the Thames Estuary is a reaction to the fact that European competitors are building bigger and better airports with more runways.
But the reality is that the UK can only sustain one hub. If we create a new one somewhere else, we would have to close Heathrow. This would have a massive impact on the economy of West London and the Thames Valley. With hindsight perhaps Heathrow was not the best location for a hub airport but we are where we are. The construction of a new airport in the Thames Estuary is not an alternative.