[2] From 2000 onwards he became involved in the defence of the British National Health Service (NHS) against successive government attempts to marketise and privatise it.

With Stewart Player he co-authored two books on the NHS and was one of the founders of a respected think tank, the Centre for Health and the Public Interest.

Leys co-edited the Labour Club's newspaper, the Oxford Clarion, and in 1951, with the late Sir Gerald Kaufmann, wrote an election manifesto called 'Labour Believes in Socialism'.

[3] From 1956 to 1960 Leys was an Official Fellow and Tutor in Politics at Balliol, but took an opportunity to return to Africa in 1960 as the first Principal of Kivukoni College, established in Dar es Salaam by Julius Nyerere to train Tanzanians for leading public roles after independence.

His last piece of field work in Africa was in Namibia in 1993–95, studying the role of SWAPO in the country's post-war political economy with Professor John S. Saul of York University, Toronto, and a team of South African and Canadian researchers.

Other activities during these years included writing commissioned reports on the creation of universities in Mauritius, the Bahamas, and Namibia; serving on a commission on the electoral system of Mauritius; co-editing with Leo Panitch the annual Socialist Register; and founding and chairing the Centre for Health and the Public Interest in London.