My husband was in complete and furious denial that anything was wrong with him - he would tell people that I was taking things and hiding them to make it look as if he was "losing his mind" or forgetting things, etc. He convinced himself of all sorts of, to him, "rational" explanations like that for what was happening with him. So I went to his GP myself, explained what was happening and his GP wrote to him and said that they were offering a free check-up to all over 70s, to make sure that they would remain in the best health possible for as long as possible - just so they could catch any possible upcoming problems in the earliest stages. The GP incorporated enough of the tests into an informal chat with my husband to see that there was cause for concern.
The same GP enabled me to get Carer's Allowance. The forms had to be signed by my husband - the snag was that there was a Medical Assessment part to the form, which had to be signed by a GP, with the diagnosis on it. So the GP simply removed that part of the form, explained to my OH that this form would be a way for us to have some extra income now that he was getting older - that the Govt would give me an allowance so I could take a bit of extra care of him, etc. - OH signed his part of the form, the GP then put pack the medical section with the diagnosis in it, and sent it off!
I do hope you can find such a sympathetic and helpful GP. I found it was best to be completely open and frank with them about things - this isn't the time for discretion. You need to let the doctor know exactly how things are.
PS. My husband is now in the late stages of the disease and in a nursing home. He never acknowledge he had dementia, and the consultant that he finally started attending felt that he was so hostile to a diagnosis, it would not be good for him at that stage to tell him. So through the years, he has never been actually told that he has dementia. He knew of course. But he didn't wan't to be told.