UKIP is gathering a “significant vote” in former coalfield communities, a leaked Labour strategy document has admitted.

And it says the right-wing party is winning over “disenchanted” Labour supporters who believe their party is more interested in attracting “better-educated, middle-class” voters.

The twin admissions come in a party document sent to Labour MPs believed to be most at risk from a UKIP surge, with advice on how to fight back on the doorstep.

It highlights swathes of the North-East where UKIP is winning at least ten per cent of the vote, although this is less than across most of Yorkshire and the North-West.

Last month, after UKIP’s stunning success in the Rochester and Strood by-election, North-East Labour MPs insisted their seats are not at serious risk and denied they were developing new strategies.

Researchers have suggested some constituencies – Hartlepool, Bishop Auckland, South Shields and Middlesbrough – may be vulnerable to a UKIP surge.

And, at last May’s European elections, the fast-rising party topped the vote in Darlington, Hartlepool, Middlesbrough, Stockton and Redcar and Cleveland.

Now the 33-page document, entitled ‘Campaigning Against UKIP’, has stressed how its popularity is on the rise from its roots in the rural South-West and East of England.

It says: “UKIP has also won significant vote shares in a wider range of areas, including in coalfield communities where support for the Labour Party has traditionally been strong.

“It is now clear that UKIP expect to poll strongly in many Labour-held constituencies and key seat targets which we need to win from the Conservatives.”

And it adds: “A major part of UKIP’s electoral success appears to have come from disenchanted supporters of all three main parties.”

They included “former Labour supporters who feel that the party has left them behind in pursuit of better-educated, middle-class, white-collar voters.”

The document sparked a row because MPs were told to focus on “moving the conversation on” to topics where Labour is stronger – such as health care or housing – when voters could not be convinced on immigration.

The advice embarrassed Ed Miliband, on the day he made a speech pledging to jail employers who undercut wages by exploiting migrants as part of efforts to address immigration concerns.

Yvette Cooper, the Shadow Home Secretary, disowned the document, describing it as “wrong” and saying: “It does not reflect what we're actually doing.”

However, the document also urged Labour MPs to “face the issue of immigration directly with identified UKIP supporters” and to “set out our immigration policy clearly”.

The advice has been drawn up for “every Labour seat where UKIP may present an electoral challenge”, with MPs given data on likely switching voters down to postcode level.