Dr Nick McKerrell, a senior law lecturer at Glasgow Caledonian University, told BBC Breakfast that returning a blank response to such a questionnaire would have “weight” behind it.
He continued: “You and I, we have human rights in that context of the rate of fair trial and the right to legal representation, even when being questioned.
“So to doing a questionnaire is quite weird because you don’t have that interaction in the same way. So theoretically, you could get no information from the questionnaire, because one of the rights you’ve got when questioned by the police is the right to remain silent.
“So you could return a blank form, I think in a criminal investigation, and it would have weight behind it. So it’s an unusual thing to do in a criminal investigation.”
Dr McKerrell said the questionnaire might be “filtering” for the police to establish where to conduct more direct interviews later. Another issue would be the length of time which had passed since the alleged offences and the fact the maximum penalty would be a fine, he said.
Dr McKerrell said: “This causes this major problem, about how do you speak to someone over things that happened months ago, when the maximum offence is a fine? So that’s one of the issues behind it, but it won’t solve the issue, it I think will have to lead to some form of more direct investigation to get just to get the information.”
It comes as North Ireland secretary Brandon Lewis said Mr Johnson was “absolutely focused on the job in hand” despite having to answer police questions over alleged Covid breaches.
He told Sky’s Trevor Phillips On Sunday: “The investigation is a matter for the police, I’m not going to put timeframes on them. They’ve got to be able to do their job independently, autonomously and see that through.
“I have to say in the dealings I’ve had with the Prime Minister, he’s absolutely focused on the job in hand, about what he’s doing for the British people.”