The government has not confirmed reports that attendees at a leaving party in June 2020 have been fined.

But one former insider told the BBC they had heard junior members of staff had been fined, while senior staff had not, and that this was "disgraceful".

No 10 has confirmed the prime minister has not received a fine so far.

One other government source said police had targeted "low-hanging fruit", and another agreed this appeared to be the police's approach.

But a Whitehall insider cautioned it was too early to say until the process was complete and all the fines had been issued.

The Metropolitan Police launched an investigation earlier this year following reports of parties in Downing Street and other government buildings in breach of coronavirus lockdown rules.

On Tuesday, the police confirmed they were issuing 20 fines as a result of the inquiry and said more could follow.

Reports have suggested the first tranche of fines related to a leaving do on 18 June 2020 for a No 10 adviser.

The police have said they will not be disclosing the names of those who are receiving a fine, nor the events to which the fines relate.

Civil servants have not been provided with help for legal costs and are being advised to pay any fines they receive, while senior staff and politicians have paid for private legal advice.

A recipient can contest a fine, in which case the police will review the case to decide whether or not to withdraw the fine or take the matter to court.

The prime minister is known to have attended at least three of the events being investigated by police and his wife Carrie Johnson is also reported to have been at some of them.

Speaking to the BBC, Labour leader Sir Keir Starmer said he agreed with the "general argument" that families should not be dragged into politics.

But he said the public was entitled to know if the wife of the prime minister who had set the rules the rest of the country was following had been fined for breaking them.