Lee Kuan Yew said he agreed to Operation Coldstore to clinch merger – which is a political matter and not because of any security issue. In a letter dated 12 February 1963 to Lord Selkirk, Lee Kuan Yew said:
It was because of your Government’s firm assurance given by your Deputy endorsing the view of your High Commissioner in Kuala Lumpur that if the arrests were not agreed to, then merger and Malaysia would fail that made us agree…… It was because of this appraisal of the Federation position by your Government and the assurance that you would dissuade them from departing from the publicly agreed terms that we agreed to the decision of the ISC [The ISC decision referenced is the mass arrests of Operation Cold Store. ]
Lee Kuan Yew 12 February 1963 Letter to Lord Selkirk