Just over three decades ago Harold Wilson campaigned for a 'yes' vote in the 1975 European referendum.
He passionately believed it was in the national interest for the UK to stay in the European Common market, as it was then called. But not all of his Labour colleagues agreed. Some of the most senior members of Wilson's Cabinet campaigned for Britain to pull out.
Wilson, ever the pragmatist, knew his best chance of keeping his Government together was to allow his Cabinet to campaign for the outcome they believed in.
There are some obvious parallels with the referendum next month. David Cameron wants to remain in the European Union but Michael Gove, Chris Grayling, Priti Patel and other Tory Ministers are demanding we leave. Once again, collective responsibility has been lifted so Government Ministers can campaign for different sides.
But thirty years on, there is one big difference. Because this referendum has been hijacked by one man who never fails to place political ambition before principle.
Boris Johnson has decided to use the EU vote to further his own career and force his way into No 10 - regardless of the cost to the country and seemingly his own party.
It is cynical. It is short-sighted. It is selfish. And I believe the British electorate will see through it.
I don't agree with Michael Gove about anything. I don't have much time for Chris Grayling or Iain Duncan Smith. But at least they are expressing a sincerely held view when they claim the UK would be better off outside the EU - no matter how misguided they are to believe it.
The same cannot be said of Boris Johnson.
Just two years ago he wrote: "leaving the EU will be globally interpreted as a narrow, xenophobic, backward-looking thing to do".
Now he is the cheerleader for the Leave campaign.
The truth is every political calculation he makes is judged against one criteria - whether it will increase his chances of becoming Prime Minister or not.
He is campaigning for Britain to leave Europe behind because he wants to be the darling of grassroots Tories who generally dislike the EU. He believes they will carry him to Downing Street on wave of anti-European euphoria. He is wrong.
Michael Heseltine was right to say he has lost his political judgement.
Boris Johnson will always put his own interests before the interests of his country. That's why he is not fit to be Prime Minister.
Tom Watson is deputy leader of the Labour Party and MP for West Bromwich EastSuggest a correction