Image copyright Getty Images Image caption WPP chief Sir Martin Sorrell says rises in revenue and sales caused by Brexit are "false gains"

Advertising giant WPP has said slowing revenue growth in the UK may indicate "the first signs of Brexit anxiety".

Overall, it reported third-quarter revenues of £3.6bn, up 3.2% compared with last year, down slightly from the 3.5% growth rate in the second quarter.

But in the UK, revenues grew just 2.1% in the third quarter, down from 3.5% in the second quarter.

Sales were up in sterling terms, but chief executive Sir Martin Sorrell told the BBC these were "false gains".

The pound has lost nearly a fifth of its value on global currency markets since the UK voted to leave the EU in June.

WPP is the world's largest advertising group. It has 86% of its business outside the UK, so its sales there, when converted into sterling, showed a marked increase.

'Tough sledding'

Overall sales for the July-to-September period went up 23.6% to £3.1bn. But when adjusted to take account of currency moves, the increase was just 7.8%.

"If the value of the currency falls, it's rather like the country's stock price falling," Sir Martin told BBC Radio 4's Today programme.

"We have to watch what impact Brexit is going to have in the fourth quarter."

He added: "All in all, it's a good set of numbers in the third quarter, but it's tough sledding. There's low growth, low inflation, and our clients are very focused on costs."

Sir Martin also weighed in to the speculation over the future of Bank of England governor Mark Carney, who has said he will reveal by the end of the year whether he will leave in 2018 or stay on until 2021.

"I really hope he stays, because he's done a stellar job," Sir Martin said.