BORIS Johnson is expected to use a "unique defence" when questioned by police about his involvement in Downing Street parties with the SNP saying he is attempting to use a "loophole" to get out of it.

The Metropolitan Police are handing out letters to 50 people as part of their investigation into lockdown-breaking parties in Downing Street and across Whitehall.

The Prime Minister is understood to have lined up a lawyer to help him defend his role in parties in Downing Street, 12 of which are being investigated by the police for breaches of Covid laws with Johnson understood to have been at six events.

The lawyer is understood to be an expert on Covid regulations and Johnson will be personally paying for their services.

Lawyers have pointed out that the Prime Minister could argue Downing Street is both Johnson's workplace and his home. The rules at the time made it an offence to be outside your home without a reasonable excuse.

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A source told The Times that the PM "will not be winging it" and will take private legal advice due to his "unique legal situation".

Other staff implicated in the scandal are also understood to be taking legal advice but do not have the same unique defence as the PM.

The PM's "unique" defence will not however stretch to claims that a party was held in his flat above No 11 Downing Street to celebrate the departure of his former top adviser, Dominic Cummings, on November 13, 2020.

SNP Westminster leader Ian Blackford has said the news of Johnson's excuse "beggars belief" that he is trying to find a loophole to "wriggle off the hook".

Blackford said: "Boris Johnson must distance himself from this extraordinary threat to the police.

"It beggars belief that the Tories think the Prime Minister should get special treatment - or find a loophole, within a technicality, to wriggle off the hook. Going down either path would do serious and lasting damage to any remaining public trust in the UK Government.

"No-one is above the law, not even Boris Johnson - no matter what he might believe. He's been caught red-handed breaking the rules, lying, and misleading Parliament. He is not fit for office - and if he won't resign, then Tory MPs must remove him."

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The 50 letters being sent by Scotland Yard out are obliged to include the standard caution for suspects that they are entitled to take legal advice before responding.

The letters are expected to be sent out today with Dame Cressida Dick saying on Thursday, before she dramatically stepped down as head of the Met, that it would be inevitable that some of the 50 would receive fixed penalty notices for their involvement.

The Met has said that recipients will have seven days to answer the formal questionnaires and outline whether they have a "reasonable excuse" for attending.