pension credit is the most underclaimed benefit with as many as 1 in 3 who are entitled to it failing to claim it. Use the pension credit claim line they are very helpful. Or just the AgeUk help line that is on the link to help you claim pension credit they are the experts and really know the system.
there doesn't seem to a be a black and white area re these pensions, state, pension credit, housing benefit, what you have in the bank - etc etc. Nobody seems to know exactly what people are entitled to. That's my opinion.