Consumer confidence in Britain has taken a dive in the wake of the country's decision to leave the European Union.

In a one-off survey to gauge the impact of the referendum result, market research firm GfK says its core index of consumer confidence dropped by 8 points to minus 9 in July. The decline was the biggest in 21 years.

The survey also shows that sentiment has sunk among both those who voted to remain in the EU and those who voted to leave. The measure for so-called "remainers" was minus 13, while "leavers" were slightly more optimistic at minus 5.

The online survey of 2,002 respondents was conducted between June 30 and July 5. The referendum on June 23 saw 52 percent voting to leave the EU.