Who has been to the doctors about their hoarder relative?

A few years ago my mother reassured us that dad would stop hoarding once we put all his books in the garage of our home  (not his). 2 deaths, one wedding and 2 grandchildren later the living room has spiralled into jenga again but with more unusual objects (and yes the garage is full). My dad has discovered gum tree and got his hand on a uni cycle and last week got another from a charity shop. 

Where the hell is he going to use it ? His garden and house is unsafe, that leaves the public road.
I am thankful for the rain because it means the Sunday car boot sales no longer run but I am worried that now my dad is getting to grips with technology a lot of his hoard will be delivered by courtesy of Royal Mail. I have pretended to not know how Ebay works to discourage my dad form using it.

I'm thinking now is a good time to book him for a GP appointment and hopefully get a referral for CBT counselling. He has given up on work (self employed) anyway. How does one broach the subject to a hoarder about seeing a doctor and how have GP's in the UK responded? A
If I make an appointment about my concerns for my dad what can my GP do?
Any advice would be appreciated.

For the sake of the children?

I have not blogged on here for a while but i have a lot to say today,There have been changes in our family which has actually given our dad an opportunity to strenghen his hoarding habit from worse to dire.  Becoming a granddad or having to borrows some other persons  house for a funeral would motivate a normal and considerate soul to make their home civilised so that people can sit. Any smidegen of a dialogue about the problems a clutter house is met with angry rhetorics about other issues.
Since 2009 we restored the living room to a normal room and twice he has filled it with belongings mostly form carboot sales. This has gone from books to garden and DIY tools and gym equipment. Even random bikes and scooter,

Family deaths and births have not motivated him to take actions. He complains often about the house being dirty but does not acknowledge it is not my mums job to spend 3 hours to move objects so she can vacuum them. I am worried that when my dads grand children come to the house they will be hurt and of course he would acknowledge it is bot his fault (do other hoarders play the blame somebody else game?). Heck at one point there was a treadmill right next to the door with a 3cm gap to get into the room (Health and safety) and what with me being clumsy and visually impairedI nearly fell, my dad told me to look where I was going and not to break his machine! yes teh machine not me. I wish I could have filmed  it and shown him how irrational he has become.... and he says I have no common sense.

Since I  moved out in 2011 I have had no respiratory problems in fact I don't have asthma anymore!
My dad gets a lot of sneezing fits and will never attribute this to his excess belongings. My nephews toys will not be able to fit in his garage of his dad's giyse because granddad has filled it with his useless junk which will decay and cause more problems and waste others time.