The Centre Union (Greek: Ένωσις Κέντρου (EK), romanized: Énosis Kéntrou) was a major centrist political party in Greece, created in 1961 by Georgios Papandreou.

It had an official constitution, membership provisions, professional cadres, national conventions, a youth wing and formal procedures for the succession of leaders.

[5][6] King Paul, in accordance with political traditions in Greece, appointed a 'service' government headed by the chief of the royal household, General Konstantinos Dovas, to oversee the campaign period to ensure impartial conduct of the election as it was feared that the ruling party may try and tamper with the results.

[7][5] On 2 December, the socialist parties and all but nine Centre Union deputies were absent from the State opening of Parliament in order to protest what they believed to be an illegal administration.

Duly, he declined an invitation to a Court Ball celebrating King Paul's sixtieth birthday on 14 December 1961, replying, "Mr Georgios Papandreou will not be attending."

[5] Karamanlis’ position was undermined further when, on 27 May 1963, Grigorios Lambrakis, a left-wing deputy from Piraeus, was murdered by two men wielding clubs in the course of a peaceful protest.

[8][9] The crisis atmosphere was heightened when Karamanlis began having spats with King Paul over a state visit to England that was set to take place in the summer of 1963.

Karamanlis, after reaching no agreement with the king regarding the matter, submitted his resignation[10] and suggested that diplomatist and outgoing ERE minister Panagiotis Pipinelis should be entrusted with the premiership and that elections should be held immediately.

Eventually, after five days of consultations, the king called on Pipienlis, who he knew would enjoy the support of all 180 ERE deputies (thus constituting a majority), to form a government.

This was not what the Centre Union had bargained for, as Papandreou denounced the new government as "inspiring no confidence in its ability to hold fair elections."

[11] With the state visit safely behind, Pipinelis demanded and obtained a second confidence vote; shortly thereafter, a new electoral bill was introduced to the chamber providing for another system of 'reinforced' proportional representation.

On 26 September, Prime Minister Pipinelis was summoned by King Paul, who handed him the royal decree dissolving Parliament and ordering elections for 3 November.

The Centre Union's victory can largely be credited to the subsiding of anti-Communism, which had flared up in the years following the Civil War and growing unemployment.

The 1964-1965 government, headed by Papandreou, enacted overdue reforms catered towards the lower and middle class by increasing pensions and prices for farmers; the system in which elections take place in the General Confederation of Greek Workers was made fairer.

[2][18][19] Papandreou and King Constantine II’s (Paul died in March 1964) relationship began to break down over disagreements on the handling of the armed forces.

[2] Initially, Papandreou retaliated against politically active officers by moving them as far away as possible from Athens, blocking their promotions or forcing their retirement,[19] but he could only do so much without occupying the Defence Ministry as well as that of Premier.

Papandreou, enjoying a healthy parliamentary majority, came to the King and demanded that he be made Defence Minister while holding the Premiership as well which was a prerequisite of replacing the Chief of Staff.

[21] An end to the crisis seemed in sight when, on 20 December 1966, Papandreou, ERE leader Panagiotis Kanellopoulos and the king reached a resolution: elections would be held under a straightforward system of proportional representation where all parties participating agreed to compete, and that, in any outcome, the command structure of the army would not be altered.

[22] Despite the crisis subsiding early on, on 21 April 1967, a month before the scheduled elections, a clique of relatively junior officers headed by Georgios Papadopoulos took over in a coup d'état.

[23] Papandreou instead formed the Panhellenic Socialist Movement (Panellinio Sosialistiko Kinima, PASOK)[24] and in the 1977 election, it eclipsed the centrists as the second largest party in parliament.