The building was given to Robert Walpole, widely regarded as the UK’s first prime minister, by King George III in 1732.
Lord Walker, the boss of supermarket Iceland and a former adviser to Sir Keir, told the Financial Times on Friday that Number 10 was no longer “fit for purpose”.
He said: “I think we should turn it into residences, or a museum. It’s a national treasure. It’s amazing. But it’s ridiculous.
“It’s just a Stuart-era building, not fit for purpose. It has tiny, tiny meeting rooms, all on different levels. There are hazards.”
Lyons, who led Sir Keir’s communications operation from October 2024 to September 2025, posted on LinkedIn that “Lord Walker is 100% right”.
He added that staff were “deeply envious” of other departments and described Number 10 as a “gloomy, mice-infested, bomb-curtained rabbit warren”.
Lyons added: “Moving out was something that was discussed when I was in 10 Downing Street.”