Merton near Bicester hosts the championships following last year's cancellation due to the foot-and-mouth disease outbreak.

The event, which runs until Saturday, has attracted about 150 teams from all over the country.

A total of 15 teams will go on to represent England in the international championships in Ireland later this year.

The trials are organised by the International Sheep Dog Society based in Bedford.

A spokeswoman from the society said: "It's a huge relief that the national trials are taking place after the problems last year with foot and mouth."