Jane Aitchison was selected in a members’ vote as Labour’s general election candidate for Pudsey, held by Conservative MP Stuart Andrew with a 331 majority.
Ms Aitchison, who was backed by key Jeremy Corbyn allies John McDonnell and Jon Trickett as well as the Momentum campaign, said that “out of context” her Twitter post about the Prince of Wales “could look bad”.
She admitted deleting the tweet, which appeared to link to a 2013 report about the tax affairs of Charles’s Duchy of Cornwall.
But she told The Yorkshire Post: “I don’t remember the context of it, I suspect that it was probably at a time when Benefits Street had just been launched or something like that and it was probably in a context, it probably didn’t sound the same four years on.”
Asked about her use of the word “scum”, she said: “What I would describe the Royal Family as is people who need to pay their taxes, like everyone else.”
She promised to focus on tackling NHS waiting times and “expensive” and “clapped out” trains.
Ms Aitchison, who in 2011 left the Socialist Party, formerly the Trotskyist Labour entryist group Militant, promised to focus on the “real problems” facing people in the West Yorkshire town.
“Like the fact that people, if they are in a dire situation, lying on trolleys for over 24 hours because our NHS is in such a dire situation because of lack of funding from this Government which has allowed private companies to cream off the profits instead of funding it properly as a nationalised service,” she said.
“The fact that the rail service is so expensive that so many people are pushed on to the roads but who would rather use public transport, but because it’s so expensive and so full and so clapped out.
“Frankly those sorts of things are things we would immediately fix if we got into power and that’s why I’m doing it.”
She said Pudsey voters will see a woman who has worked for the Department for Work and Pensions for 25 years helping people in “desperate situations” and a trade unionist who has been “struggling to help people who feel bullied, or who need better pay or who need better terms and conditions”.
But Mr Andrew said her “pretty appalling” comments called into question her judgment.
He said: “I’ve had decent longstanding members of the Labour Party complain to me that the hard left are taking over.
“It sort of confirms that is the case, we’ve got someone who represents the hard left of the party.
He added: “People in the constituency are known to be very supportive of the Royal Family and the hard work they do.”