For the wealthiest tier of foreigners living in Britain, the most worrying aspect of last month’s pre-Budget report was some cryptic comments about “anomalies” buried at the end of a headline-grabbing announcement of a new £30,000 tax charge.

Immediately, many feared the worst: the prospect that their family trusts would be exposed to new capital gains tax charges. According to one London lawyer, many of his clients – including a Norwegian businessman, an Italian hedge fund manager, an Anglo-Arab ship financier and a South African – made immediate plans to leave the country.