If great university departments are those that embrace contrary opinions, UCL Planning is outstanding. For our research totally contradicts the conclusions of our colleague Professor John Tomaney (This is one big punt, 29 January). He quotes other sources suggesting that high-speed rail does not help lagging regions. Our work, based on close analysis of a big primary database, concludes that it definitively does.

Here in the UK, the 30-year-old Inter-City 125 network has boosted the economies of cities that it brought within a two-hour journey time from London, such as Manchester and Leeds. In France, the TGV has brought Lille within one hour of Paris, enhancing its transformation into a knowledge-economy city and even making it attractive for Parisian commuters.

In both countries, we find there's a catch. High-speed rail does not always help old one-industry cities like Doncaster and Newport. And it can boost major cities – Manchester, Leeds, Lille – at the expense of their surrounding old-industrialised regions. But French experience shows that strong regional policies can combat this by spreading TGV service to these other towns and developing a regional TGV network.

HS2, offering fast service to places like Wigan, Preston and Blackpool, could potentially galvanise such places. But it will need other policies to exploit these opportunities – and, in sharp contrast to France, we've just abolished our regional planning apparatus.

Professor Peter Hall and Chia-Lin Chen

Bartlett School of Planning, UCL

• Peter Johnston's claim (Letters, 30 January) that Brunel was responsible for converting "a couple of hundred miles or so" of the GWR from broad gauge to standard gauge in a weekend is mistaken. Brunel died on 15 September 1859; the conversion of 177 miles of track to which Johnston refers took place on 21-22 May 1892. ET MacDermot's History of the Great Western Railway (1931) suggests much preparation preceded that weekend.

Victoria Owens

Bristol