Basement extensions have become hugely controversial, particularly in Central London, and that was certainly so in one case in which the French Government tried to block such a development in the heart of the capital’s diplomatic quarter.

The long leaseholders of a listed building, which had once been home to the Russian Soviet Mission but which had been empty for some years, had begun work on a basement extension which was to be used as a museum for a collection of vintage cars. The building was next door to the residence of the French ambassador.

The local authority agreed with the leaseholders that the works were authorised by a planning permission and listed building consents which had been in place for some years. Certificates of lawful development were issued to that effect.

The French Government challenged the council’s decisions on a number of grounds. Amongst other things, it was argued that the council had failed in its duty to consult those who would be affected by the development and had no power to certify the lawfulness of works which had already been carried out.

The council conceded that it had delayed longer than it should have done before entering one of the certificates onto its planning register. However, the court found that this administrative error did not justify quashing that certificate. The other grounds of challenge to the certificates were rejected.