Gandy, 41, gained permission for the project at a tense meeting last week as millions tuned in to England’s victory over Denmark in the Euros.
The “unsympathetic” proposal was opposed by a heritage group and recommended to be turned down by sceptical planning officers. But councillors were won over after a presentation by Gandy’s partner, Stephanie Mendoros, who is a barrister specialising in crime and family law at Staple Inn Chambers.
Speaking by videolink, she argued that the couple wanted to maintain the “character, beauty and integrity” of the building and “make it fit for our growing family and for future generations”.
The property, classified as a building of townscape merit, was built in 1927 by Arnold Smith and Cecil Brewer for the American film director Edwin Middleton. Council officials and the Mortlake with East Sheen Society argued the extension should be blocked as it was “overbearing”, “unsympathetic” and would harm the surrounding conservation area.
The couple bought the derelict property for £4.4 million in November last year. It could now be worth more than £10 million.
Ms Mendoros stressed the key features of the property will not be changed and that planning permission for a single-storey extension had already been given. She argued adding another storey on top of this would only create an extra bedroom and bathroom, while the new double-height extension would hardly be visible from nearby streets.
She told councillors the plan was supported by neighbours. The committee approved it by a vote of six to two.