Four hundred children's guardians have said they will not join the Children and Family Court Advisory and Support Service, according to the guardians' professional association.

The National Association of Guardians Ad Litem and Reporting Officers has received 400 letters from guardians, who are self-employed, saying the salaried employment contract offered by Cafcass is "unacceptable", following its decision to renege on offering self-employed contracts.

The number represents more than half of the 750 guardians, threatening to bring the service to the point of collapse from August.

Cafcass's contingency plans include a recruitment campaign launched this month for "family court advisers" in child care law proceedings. A Cafcass spokesperson said it had already had 500 expressions of interest.