Eton College, which has owned the plot of land on which the buildings are sited since 1449, has lodged an application with Camden Council in north London to knock down the cottage and build three houses.
The plot, at the corner of Eton Road and Provost Road in Belsize Park, is one of the last fragments of a swathe of land given to the college by Henry VI 500 years ago.
Mona Brearley, who lives next door with her husband, the former England cricket captain Mike Brearley, has written to all local residents asking them to join a campaign against the plans. The actors Bob Hoskins and Derek Jacobi, as well as the Oasis singer Noel Gallagher and Helena Kennedy QC all live in surrounding streets.
"This is a conservation area and these buildings and the land they stand on are absolute gems," Mrs Brearley said. "I do think Eton should have the courtesy to talk to the residents about what they want because there is great strength of feeling about it."
It is not the first time the denizens of leafy north London have swung into action and petitioned Camden Council when the modern world has threatened to encroach upon their graceful houses and tree-lined streets.
Residents in Hampstead, having failed in the "Burgher Off" campaign to keep McDonald's out of the High Street, are currently trying to save the area's last authentic coffee bar, The Coffee Cup.
Now the fight to preserve the beauty of the area has moved south to Belsize Park. It is the fourth time that the school has applied to demolish the cottage and build on the site. One application was turned down last September and the others were withdrawn.
"They have totally neglected the house in the past. It could have been a beautiful home in its own right, but now it is a terrible mess and I think what they are doing amounts to vandalism," Mrs Brearley said.
However, May Bass, secretary of the Provost Court residents' association, said the cottage should be renovated. "What is the point of having a conservation area if you are not going to conserve anything.
"The cottage is not beyond redemption and they should do it up. The grounds could be beautiful and they provide a welcome bit of greenery."
Anthony Culligan, said that if Eton College authorities insisted on demolishing the cottage they should build something of a similar size. "You cannot just knock down a building in a conservation area unless you are going to do something which enhances the area and I cannot see that these houses will do that," he said.
But Adrian Harris, the estates manager for Eton College, said the three planned houses - one three-storey family home and two semi- detached houses - would complement the area far better than the run-down cottage which was too small to convert to a family house.
"We have been advised that the best course of action would be to demolish it all together and build something more in keeping with the locality. The plans for the new houses match the architecture around. It is in Georgian style, but it is not a monolith and will not involve felling any trees," he said.
He added: "I think that what we are proposing is attractive and in keeping with the area."
A spokesman for Camden Council said the application had been received and was at the consultation stage. A final decision is expected on 9 July.