The Labour Party has launched an “attack ad” against Ukip leader Paul Nuttall, who is expected to pose a real threat to Labour in the forthcoming by-election in Stoke.

Labour leader Jeremy Corbyn tweeted a video about Mr Nuttall, with the warning: “Voters of Stoke, if you value your NHS then don’t vote for this man who wants to sell it off #CarefortheNHS.”

In the footage, MEP Mr Nuttall brands the NHS is “a monolithic hangover from days gone by”.

“Unfortunately – or fortunately, should I say – we’re becoming an older population, and quite frankly I would like to see more free market introduced into the health service, because this is the way that we have to go in the long term,” Mr Nuttall adds.

The video was released as it was confirmed that Mr Nuttall would contest the seat of Stoke-on-Trent Central, left vacant after Labour’s Tristram Hunt quit politics to become director of the Victoria and Albert Museum in London. Other parties have yet to announce their candidates.

Mr Hunt was re-elected in 2015 with a reduced majority of just over 5,000 – and Ukip will see this as a very winnable seat, given that Stoke-on-Trent came out as the most pro-Brexit city in the UK in the EU referendum. Almost 70 per cent of voters there backed Brexit.

Ukip finished second in the seat in the 2015 general election, just 33 votes ahead of the Conservatives in third place, and Mr Nuttall has gone on the attack against the so-called “metropolitan elite” in Labour for "neglecting" traditionally working-class areas like Stoke.

The Labour video was tagged with the warning: “There’s one thing you should know about Paul Nuttall – he supports greater privatisation of the NHS.”

Attack ads, common in the US, have been becoming more popular in the UK in recent years.

Online advertising is free from the strict rules that govern television campaigns, with both Ofcom and the Advertising Standards Authority saying they have no power to regulate them.

In the last general election campaign, the Conservatives used an online and poster campaign of a beaming Ed Miliband outside Number 10 with former Scottish First Minister Alex Salmond to warn against handing power to the SNP in the event of a hung Parliament.

During the 2015 campaign, the Labour Party said it would not run attack ads, but would focus on “issues rather than personalities”.

But last year, Labour made an online ad featuring the then Chancellor, George Osborne, in a dodgem car to claim that he didn’t understand the importance of fair taxation.

Party sources have also announced that senior Labour MP Jack Dromey is to run Labour's by-election campaign in Stoke.