Threatened with abolition and replacement by a single- tiered system of local government, they will fight vital test cases crucial to the future of 12 other councils across England also facing abolition.
Derbyshire County Council claims the Secretary of State for the Environment rode roughshod over the Local Government Commission for England's recommendation that the existing two- tier system be retained in Derbyshire.
Lancashire CC claims new ministry directives that two-tiered systems should be retained only in exceptional cases effectively means the same thing will happen there.
The legal challenges arise out of the Government's decision to have the Local Government Commission for England evaluate whether county councils, and district councils beneath them, should be replaced by new single-tier authorities.
The issue for the commission to consider was whether increased efficiency and reduced bureaucracy would outweigh the costs of such a change. Derbyshire was one of nine county councils in the first group to be examined by the commission.
After a year-long investigation, which included a survey in which 45% of local residents opposed the change, the commission recommended that the system should remain as it is.
The Secretary of State then issued a directive in November last year that two-tiered councils should only be retained in exceptional circumstances. The commission was told to consider Derbyshire local government afresh and the County Council will next week battle to have that reevaluation stopped.
The county council wants the commission's original recommendation that the two-tier system be kept in place adopted. Lancashire CC claims the commission's discretion has been unlawfully fettered and its function subverted by the new central government directives.
Lancashire County Council's case is listed for a two-dayhearing to commence on Monday. Derbyshire County Council's case is expected to follow on Wednesday.