Self-made billionaire property tycoon, Jon Hunt, founder of Foxtons estate agents, is in a ferocious legal battle with the French ambassador, Sylvie Bermann.

The unlikely pairing, are in a dispute concerning the permissions granted for Mr Hunt's proposed mega-basement extension at his listed home in Kensington Palace Gardens - London's billionaire's row.

Basement extensions are a hot topic in London where space for development is limited and local authorities are clamping down on granting permission for them. The recent trend has resulted in a vast increase in basement excavations with many owners making lavish plans for underground swimming pools, spas, gyms and home cinemas.

How can planning decisions be challenged?

Permission is always granted subject to time limits within which it must be begun. Once it has begun development can then normally be completed regardless of timescale.

When a planning decision is refused, the applicant (usually the owner), has an opportunity to appeal by submitting an appeal to the Planning Inspectorate. When a planning decision is granted, notwithstanding objection from a neighbour, the objector has no right to appeal as they are not party to the application, instead their only option is to make an application to the High Court for judicial review.

Kensington Palace Gardens mega basement extension

Mr Hunt sought certificates from the local planning authority to confirm that he could complete the works he had started, relying upon previous planning permission and listed building consent. The certificates were granted by the London Borough of Kensington and Chelsea in April 2015.

The Ambassador unsuccessfully challenged the certificates in the high court in November 2015 arguing that the Council's decision to grant them was unlawful as the planning permissions had expired and the Council had not complied with the necessary procedures.

It is understood that the French Embassy, which has now gained support from ambassadors from five other countries who also live on the road, is taking the matter to the Court of Appeal.

They argue that this contravenes article 22 of the Vienna Convention. The Vienna Convention aims to govern diplomatic relations between countries and article 22 states that the "State is under a special duty to take all appropriate steps to protect the premises of the mission against any intrusion or damage..." 

Whilst the state may have such a duty under article 22, we expect that the Council and Mr Hunt will argue that this duty to protect has been adequately discharged when the planning and listed building consents were first considered under normal planning procedures. 

It may sound a legal technicality but the factors that must be taken into account on a planning application are far wider than the narrow legal issues which the Council could consider on the applications that it considered here.

Whilst security issues for an embassy are relevant for a planning application, the only considerations the Council could take into account when determining this case were whether the permissions had been implemented. The French Embassy seems to have picked the wrong fight on this occasion.