What about contacting Age Concern or MIND for advice?
They are agencies in the UK and might be able to refer you to the correct service or have advice for you themselves.
Not sure how long you have been away from the UK but there is a bit of press coverage about increasing problem drinkers in your Dad's age group.
Do you think a grief counsellor could help him?
Would he be open to that?
He sounds very depressed. Do you think his GP is aware?
I had a friend who had a recent hard time with her partner and alcohol was involved. He also has a significant health problem he is dealing with too.
She wrote to his GP and stated all her worries and outlined how grave the situation was and that he was hiding a lot from the doctor.
The GP sent a letter asking him to make an appointment for a 'health review' and that it might be a good idea to bring his partner.
It was handled really delicately, no pressure, no row's or shouting matches.
Could that be an option for you?
Does he have any neighbours who might be willing to keep an eye on him and check everyday he is up and about? Maybe you could contact them by letter or email?
I really feel for you being so far away and the worry of if he is alive and well each day. Its a huge burden to carry. However, don't ever feel bad. At the end of the day he is an adult, he is the only one that can decide if he wants to accept help.
I really wish you the best xx