Ireland's mushroom industry provides a stark warning to the rest of the country's economy about the damage a sustained weakness in sterling could inflict on Irish exporters, the sector most vulnerable to the impact of Brexit.

Mushroom growers rely on the UK for 80pc of sales and have been losing money since Britain's vote to quit the European Union in June sent sterling tumbling. It has now lost 19pc of its value against the euro, wiping out the Irish producers' profit margins.

Five of Ireland's 60 mushroom farms have so far gone out of business since the referendum, including two this week.