Labour asks if Conservatives broke U.K. election laws by accepting a donation linked to a Russian account.

Britain’s opposition Labour Party on Tuesday formally demanded answers in Parliament to whether the governing Conservative Party had breached electoral laws when it accepted a major political donation that documents link to a Russian bank account. Opposition leaders also asked for information about the donor’s potential ties to the Kremlin.

The contribution, of $630,225, was made in February 2018 in the name of Ehud Sheleg, a wealthy London art dealer who was most recently the Conservative Party’s treasurer. He is one of the party’s biggest donors and, through his lawyer, he has denied any wrongdoing.

Raising the question in Parliament places a spotlight on the donation and puts political pressure on the Conservative Party to respond. The money was part of a fund-raising blitz that helped propel Prime Minister Boris Johnson and his party to a landslide victory in the 2019 general election.

According to a bank alert filed to Britain’s national law enforcement agency, the donation originated in the Russian account of Mr. Sheleg’s father-in-law, Sergei Kopytov, who was once a senior politician in Ukraine’s previous pro-Kremlin government. The bank flagged the transaction as suspected money laundering and a potentially illegal campaign donation. Mr. Kopytov is a Ukrainian citizen.

On Tuesday, the chair of the Labour Party, Anneliese Dodds, demanded that the government provide information on whether Mr. Kopytov owned assets, including a Mercedes-Benz car, that had been used by people involved in the Russian state. She also asked for clarification on links that Mr. Sheleg and Mr. Kopytov might have with “key actors in the Russian state.”

“And finally,” she asked, “has electoral law been broken and, relatedly, has our national security been compromised?”

Ms. Dodds said she had also written to the chair of the Conservatives, calling for an investigation into Mr. Sheleg’s donations as well as other donors with possible links to Russia. She said she also asked whether the Conservative Party intends to keep the money donated by the art dealer.

Mr. Sheleg’s lawyer has acknowledged the art dealer and his wife received millions of dollars from Mr. Kopytov in the weeks before he gave the Conservative Party the $630,225 donation.

But the lawyer said the money Mr. Kopytov had given the Shelegs was a family gift and “entirely separate” from the campaign contribution. The Conservative Party has said that all donations “comply fully with the law.”