The Economist has just published an article (“Ordeal by Water“, 20 February) based on Policy Exchange’s proposals for an expansion of commuter transport on the Thames. The author would have been advised to cast a more critical eye over the report on which the article is based, along the lines of Adam Bienkov’s well-informed post on the issue.

The Policy Exchange report, entitled At a Rate of Knots, asserts that the current Transport for London (TfL) subsidy to Thames Clippers amounts to a mere 14p per passenger journey compared with 33p for buses. This struck me as an unbelievable claim, since an earlier report by the London Assembly, London’s Forgotten Highway, had quoted a TfL figure of 69p. So I tabled a question about it to the Mayor of London, Boris Johnson.

The Mayor replied that the most recent monthly figure from TfL is 56p per passenger journey, four times the level of public subsidy claimed by Policy Exchange. He explained the discrepancy between the two figures on the basis that it was “likely that the Policy Exchange figure has been arrived at by dividing the TfL contract payment over the whole of the Thames Clipper operation, i.e. both the supported and the commercial elements”.

In other words, Policy Exchange got their sums wrong.

I take the view that there is much scope for the Thames to play a greater role as a transport highway – but as a means of moving freight rather than passengers. This would have a positive environmental impact by reducing the number of HGVs passing through London. However, if the case is to be made for increased public subsidies to underpin a large-scale expansion of passenger transport on the Thames, it requires more than a dodgy dossier based on faulty arithmetic.