The Electoral Commission is hurriedly contacting all counting officers in the UK telling them not to send out a controversial “biased” guides to postal voters which suggest they should support the Remain side in next month’s referendum.

The news came after the regulator told Bristol City Council – which has already sent the leaflet to 47,000 homes - to stop sending out the leaflet and launched an investigation into whether the issue was more widespread.

Other voters across the country last night said they too had received the same guides, suggesting that hundreds of thousands of voters might have been unfairly encouraged to back Remain.

More than six million people voted at last year's general election alone which suggests that millions might vote by post in the EU referendum next month.

A spokesman for the Commission said: “As a precaution, we are contacting all Counting Officers to make clear to them that if they are using images the same as, or similar to, the image used by Bristol City Council, they should ensure that these are changed before any further postal votes are distributed.”

The Telegraph established on Monday that voters in Kent have received the same form as voters in Bristol, while there were reports of the forms being sent to voters in Greater Manchester, West Sussex and Hertfordshire.