The meeting for “potential supporters” of the new pro-European centrist party was led by Tony Blair’s former chief of staff Jonathan Powell and Philip Collins, who was the ex-prime minister’s speech writer. Ms Riley and Ms Rowling were said to be among 50 attendees at the reception which was held at the London offices of the author’s agent Neil Blair. Mr Powell and Mr Collins told guests they aim to launch the Blairite movement – which has not yet been named – after Brexit, claiming the party could win up to 100 seats.
An invitation to the evening insisted Britain “desperately needs” a new party.
It read: “We are hosting a drinks reception at 7pm on Tuesday 5th February for potential supporters of a new political movement that Britain desperately needs. This is an initiative led by Jonathan Powell and Philip Collins.
“Britain is stuck. The promise that the next generation will be better off than their parents is broken. Inequality is tearing the country apart.
“Housing is too expensive, earnings are static and the quality of work is too poor for too many.
“The world is changing fast and we’re retreating from it… the old parties cannot face the future because they have run out of answers, energy and leadership.
“That is why Jonathan and Philip are building a new political movement to move Britain on to a better politics.”
At one point, there was applause when it was suggested that the Harry Potter author – who is a vocal critic of Labour leader Jeremy Corbyn – head up the rival party.
A source told the Mail on Sunday: “There was a presentation which lasted for about 45 minutes and was followed by a Q&A.
“The organisers emphasised the need for a charismatic leader for the party to succeed. But they made it clear they are unsure who that is at the moment.
“One attendee suggested J. K. Rowling – which got a large round of applause.
“They emphasised that a new centrist movement has the opportunity to attract people with a more nuanced approach to politics and life – and that is why they believe they can succeed where the SDP failed.”
Mr Powell and Mr Collins also raised Labour’s anti-Semitism crisis as another reason for the launch.
Ms Riley, who is Jewish, has been attacked by Mr Corbyn’s supporters for criticising his failure to get a grip on the row.
The Countdown star revealed last month that Channel 4 were forced to give her extra protection after she received threats from the hard-left.
Plans for the Labour rebel movement come after a new pro-Brexit party, backed by former Ukip leader Nigel Farage, was officially recognised by the Electoral Commission last Friday.