Former Prime Minister Harold Wilson personally intervened when a council's efforts to prevent rabies threatened to banish his dog from the family holiday home.
Documents record the phone calls and urgent letters between the premier and the Scilly Islands council.
The exchange began when newspapers reported on January 14, 1976 that the council had proposed a ban on visitors' dogs to prevent the spread of rabies from France.
Wilson had a holiday home in Scilly, and the documents show family pooch Paddy's attendance there was non-negotiable.
A letter to Wilson from Roland Phillips, chief executive of the council, dated January 14, says a colleague "rang me late last night to warn me that the Committee's deliberations yesterday on the subject of Rabies was blowing up into a lot of stupidity hinging round your poor unfortunate dog".
Phillips said he understood Wilson was "furious", and added: "I can well appreciate it."
The letter explained concern about animals coming ashore off yachts from the Continent and said the council had discussed whether hoteliers could be persuaded to refuse to accept guests with dogs.
He wrote: "There was absolutely no intention of trying to effect any control over "residents" dogs, in which category you would, of course, come, and the whole arrangement would, of course, have to be entirely voluntary."
He went on: "We can't for the life of us understand why people want to bring dogs on yachts but they seem to want to do so.
"Last year we prosecuted successfully a Frenchman who, quite blatantly, perfectly under-standing all the information that
had been given to him on arrival, decided to exercise his dog on the Lifeboat Slip one morning."
He concluded: "Our sincere apologies for the way in which all this has been blown up into a lot of nonsense around you - I suppose it is inevitable these days!" The letter seemingly failed to reassure Wilson, and Downing Street drafted a number of letters in response.
A note to Wilson headlined PADDY, dated January 16, reads: "Below is a letter for your signature in reply to one from the Chief Executive of the Scilly Islands Council explaining that they have no intention of banning Paddy from the Islands.
"A hand-written note signed with the initials HW reads: "Please see draft and have worked at quickly."