Why did UK Prime Minister Harold WIlson think that MI5 was spying on him?

A figure on the Labour Party's 'soft left', Harold Wilson's victory in the 1964 UK election saw the implementation of various social reforms, as well as the re-nationalisation of the steel industry and the banning the security services from bugging the phones of MPs. Meanwhile, in foreign affairs, Wilson angered the United States by refusing to send troops to Vietnam. Two years into his term, Wilson called a new election in 1966, winning a more decisive majority in parliament. However, various problems began to emerge, including the mobilising of the far-right.
In 1967, the National Front was established, with the group combining street violence and contacts with the right wing of the Conservative Party. Although much of their hierarchy held anti-Semitic beliefs, the NF moved away from campaigning openly against Jews to focusing their attention on new migrants from the empire, who had helped restart the economy after the Second World War. Meanwhile, in the halls of power, a major moment came in 1968 when high-ranking Conservative Enoch Powell gave the 'Rivers of Blood' speech, warning of violence from immigration. Powell was sacked from the shadow cabinet but stays in party, and remains influential in part through the Conservative Monday Club, a hard-right pressure group which had links to the National Front.
Powell's speech gave legitimacy to far-right, which began to increase its efforts to recruit supporters in traditionally Labour voting working-class neighbourhoods. The increasing racial turmoil was compounded by an unexpectedly bad balance of payments on the eve the 1970 election, which Wilson lost. Four years later however, Wilson came back, beating the Conservative Party's Edward Heath. During his second term, Wilson would become increasingly paranoid, convinced that elements of the British state were working to subvert his administration.
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Over the following decades, it would be alleged that there indeed had been a conspiracy against Wilson, coordinated by MI5 in an operation which broadly mirrors accusations about NATO-sponsored stay-behind networks in Continental Europe. In June 1974, the army had conducted a secretive training exercise at an airport, without informing the Prime Minister of their plans.
Supposedly, the exercise was training for a potential IRA attack on an airport, with the conflict in Northern Ireland being the source of more explosive allegations of the plot against Wilson. Back in August 1969, less than a year before Wilson's first defeat, an Ulster Loyalist march into Catholic areas in Derry led to outbreaks of violence across the region, and is generally credited as being the beginning of The Troubles. According to later claims, the subsequent decades of conflict had been encouraged by MI5 as a means of weakening Wilson.
The Ulster strike had been supported by Loyalist paramilitaries, including the Ulster Defence A, which had links to the wider far-right in the UK. Along with the escalating clashes between groups such as the IRA and UDA, back in England, Wilson's administration also had to contend with extremism at home, along with continuous leaks from inside his own office. By 1976, he had had enough, and resigned, with party right-winger James Callaghan succeeding him.

[@FrankBoothPBR]

Angelton was paranoid of all British intelligence after he considered Phliby a true friend. The thought of Angelton CIAs head of counterintelligence volunteering intelligence to Philby the head of the anti-soviet section of MI6 and Russian double agent and at one time considered to be the next chief of MI6 is so completely mind boggling it's crazy. Philby either had nerves of steel or was drunk 100% of the time, possibly both.

[@MarkHarrison733]

British troops served in Vietnam.