I have British passport which recently expired. The lag time for renewal means it will not be ready for my holiday to Britain. Am told by visa office I don't need visa because I am citizen. But I will be travelling on my other passport (which stand alone needs a visa?
As a citizen you don't need a visa to enter the UK, since you have a legal right to do so. You would need evidence of citizenship, but an expired passport is one possible mechanism to do this. Since your second nationality is one which would require a visa, your biggest difficulty may be convincing your transportation company (airline/ferry company etc) to let you board in the first place.