As an NUM activist, he became a flying picket, moving around Wales at the behest of Arthur Scargill, in the 1973 and 1974 strikes to oust Prime Minister Edward Heath's Conservative government.

O'Sullivan explained to his members at Tower the probable result of not fighting the closures, and gained 99% support: I phoned Emlyn Williams who was President of the South Wales area of the NUM and told him of my unease.

[1] O'Sullivan later led the group of miners leaders against a national ballot during the strike, as it would have needed to include the Nottinghamshire branch, who would have voted against it - its leadership later formed the breakaway Union of Democratic Mineworkers.

He disclosed on the closure of Tower Colliery that he and his family knew at the time of the strike that their private home telephone had been bugged by MI5.

They no longer waited for their miner husbands to come home on a Friday and hand over a pay packet.

In October 1992, the Conservative Government as part of a privatisation program of British Coal, announced closure of 31 of Britain's 50 working mines.

However, in 1994, after its closure was ordered by Michael Heseltine of the Conservative government of John Major, the Tower miners decided to mount publicity campaign.

His famed 1994 quote later became a line in a locally produced opera by Welsh composer Alun Hoddinott:[5] We were ordinary men, we wanted jobs, we bought a pit.O'Sullivan was probably nearer to the truth in that quote than any other reason for buying the pit, as local unemployment then was 30% in Aberdare, and would have risen to 40% had Tower and its 400 employees joined the dole queue.