The FTSE 250 index opened down 11.4 per cent this morning, its worse ever fall, after the UK voted unexpectedly to leave the European Union.
It has recovered somewhat in the 30 minutes of trading so far, moving to just 9.7 per cent lower.
Unlike the FTSE 100, the 250 index is largely made up of domestic focused companies, who sell most of their products and services in the UK.
The FTSE 100 makes the majority of its money internationally and can be more easily buffeted by international headwinds.
The FTSE 250 has suffered worse than the FTSE 100 over the last 12 months, around 10 per cent down on where it was this time last year, while the FTSE 100 is 6.7 per cent lower.