Beleben has been looking at the NAO report into HS2.
In particular he says:
The report did not address the effects and risks of Great Britain leaving the European Union, and it would appear that the NAO considered it a zero probability event. In the non-binding referendum that took place on 23 June 2016, 51.9% of votes were for Brexit. The value of sterling fell after the referendum result became known.
Although presented as a ‘British’ project, HS2 would be largely built with imported materials, equipment, and labour, so forex risks from Brexit could be significant. If there were a ‘tariff war’ and restrictions on foreign labour, there could easily be a cost uplift of £10 billion or more.