Change doesn't come easily to the northern beaches and former Labor premier Barrie Unsworth is doing his bit to fight it, finding an unlikely ally in Liberal Bronwyn Bishop.

Taking aim at the proposed B-Line bus service, Mr Unsworth has tapped into a vein of discontent in the Liberal heartland, which is broadly brewing around the new bus service, council amalgamations and the fears of overdevelopment in the northern beaches.

Calling the B-Line a "Trojan horse" for development, Mr Unsworth has slammed the expected privatisation of the new bus corridor between the northern beaches and the CBD, and the decision to build a new bus stop at Mona Vale's Village Park.

"We've had government bus services for as long as anyone can remember. We're all happy with the operation of the buses now," Mr Unsworth told Fairfax Media.