Tony Blair is expected to be quizzed about the financial dealings of Culture Secretary Tessa Jowell.
She is facing questions about the business affairs of her husband, David Mills.
She denies any wrongdoing.
International lawyer Mr Mills denies taking a Ј344,000 bribe from Italy's Prime Minister Silvio Berlusconi.
Shadow Commons leader Theresa May wants a ruling on whether Ms Jowell breached the ministerial code of conduct.
The prime minister will appear at No 10 with Ms Jowell to mark the publication of a report about women and work.
'Good minister'
The Sunday Times alleges it has identified a link between a loan secured on a house jointly-owned by the couple and money which Italian prosecutors allege was a bribe.
Ms Jowell co-signed a mortgage on the Ј700,000 home in Kentish Town, north London, which she jointly owns with Mr Mills, but said the deal did not mean a conflict of interest.
"I agreed that we would take out a loan on our house. That is not unusual, it's not improper, and it's certainly not illegal," she told reporters outside her home on Sunday.
The Lord Chancellor, Lord Falconer, says he is confident Ms Jowell has adhered to the ministerial code of conduct.
"She's been a really good minister at every level. She should stay in her job," he told BBC's Politics Show.
Italian officials say Mr Mills, 61, was paid to give false evidence in court for Mr Berlusconi.
Mr Mills admits writing a letter to his accountants where he appears to be describing a payment, but claims he was inventing a scenario to get tax advice.
In a statement, Ms Jowell said: "I signed a charge over our jointly-owned home to support a loan made to my husband alone by his bank.
"I am satisfied that no conflict of interest arose out of this transaction in relation to my ministerial duties.
"As is standard practice in relation to legal proceedings, it would be inappropriate for me to comment further."
But Ms May said it was not essential to know about the Italian investigation into Mr Mills.
She said she was concentrating on whether the ministerial code had been breached by Ms Jowell.
"I don't know what she knew about the financial, those financial transactions," she said.
"But all I'm asking is, has the ministerial code been adhered to, particularly obviously in relation to any requirement to notify in relation to financial transactions."
(BBC)
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