Downing Street has refused to publish the names of people who visited Number 10 during Covid rule-breaking parties.
Officials dismissed a request from Lib Dem Chief Whip Wendy Chamberlain for visitor logs, claiming it was "vexatious".
The word, increasingly used by public bodies to refuse Freedom of Information requests, means to "cause annoyance".
No10 said it would be "burdensome" to provide the information - and accused Ms Chamberlain of using a "scattergun approach designed for the purpose of “fishing” for information."
They added: "While we acknowledge that there may be a wider public interest and objective value in some of this information, disclosure would be of limited value given that there are already independent investigations taking place considering these matters."
Ms Chamberlain said: “I was a police officer for 12 years, so I'm used to seeing people who know they've done something wrong trying to wriggle out of it.
“Being told my request for basic information such as who entered Number 10 is ‘vexatious’ takes me back to those kind of interviews. The difference is, I'm used to getting these responses from offenders, not the Government of our country.
“Their attempts to evade scrutiny tells me there’s clearly something they want to hide. They must come clean and the fact that Boris Johnson continues to do all he can to cling on to power is shameful.”
Number 10 confirmed on Friday that the Prime Minister had completed his partygate questionnaire and handed it back to police.
The Prime Minister is believed to have attended up to six gatherings that are being looked into by police inquiry into parties thrown by the government during lockdown.
It has been reported he has hired his own personal lawyers to help with answering the questions.
