The first music festival at Blenheim Palace, in Woodstock, will now stretch to four days and feature a famous international star - although the organisers are keeping their identity secret for the moment.

Members of West Oxfordshire District Council's licensing sub-committee agreed to grant a public entertainments licence for Sunday, July 4, to add a further night to the festival, which has concerts on the Thursday, Friday and Saturday nights.

Tickets for the first night, featuring Jamie Cullum and Katie Melua, have sold out, but there are still tickets available for the show starring Van Morrison and Joan Armatrading, on July 2, and for the concert by the London Symphony Orchestra, on July 3.

The palace's chief executive, John Hoy, said: "An opportunity has arisen to stage an additional night for the festival in order to accommodate an international artist of the highest repute, who I cannot name at this stage. They will fully fit the profile of the venue and enhance the reputation of the festival in this inaugural year."

Each concert will seat 10,000 people in the main courtyard of the palace. The shows are part of a series of events to mark the 300th anniversary of the Battle of Blenheim, where British troops were led by John churchill, the first Duke of Marlborough.