This book is the result of a conversation I had with the late Mr S.R. Nathan, the distinguished former President of Singapore, whom I had first known in Johor Baru where he was working for the Public Works Department (PWD) before he moved to Singapore and eventually became President of Singapore. I was then in the Johor Special Branch. Much later, when he moved to Singapore and became President, and I was no longer a Special Branch officer but had become a Visiting Senior Fellow at ISEAS – Yusof Ishak Institute, Singapore, we renewed our acquaintance and we used to meet sometimes, at his invitation, in his office at the Singapore Istana to discuss intelligence matters in which, having been at one time Director of the Security and Intelligence Division of the Singapore Ministry of Defence before he became President, he maintained a keen interest.

He knew that I had written a book on the Malayan Special Branch, and he asked why I did not write a similar study about the Malayan Security Service (MSS), which was the domestic intelligence agency established by the British covering both Singapore and Malaya from its headquarters in Singapore when they returned to Singapore after the Japanese surrender in August 1945. When I said I was interested, he arranged for me to be allowed to use the digitized records of the MSS that were held by Singapore's ISD (Internal Security Department) in the ISD Heritage Centre, Onraet Road. It was then I started my research on this book, Dalley and the Malayan Security Service, 1945–48: MI5 vs. MSS, although as I explained to Mr Nathan, I would perhaps sometimes have to rely on some of the background material I had used in my earlier paper “The Malayan Security Service (1945–1948)” and book Malaya's Secret Police 1945–60: The Role of the Special Branch in the Malayan Emergency, although I would incorporate in my present writing, wherever necessary, further information and insights which had come to light since then.

In writing this study, full use has therefore been made of the fortnightly reports of the MSS's Political and Security Journal (PIJ) and its Supplements, complete runs of which have been digitized and held in the ISD, which I did not have access to when I wrote about the MSS so many years ago.