No.
The theory involves Harold Wilson being a Communist Spy.
There is, btw, absolutely no evidence that would make a reasonable person even think about thinking about taking the idea seriously.
1. There was nothing suspicious about Gaitskell's death. Tragic and sudden, yes, but not suspicious. Least not to anyone sane.
2. At the time of Gaitskell's death, the Deputy Leader of the Labour Party was George Brown. Brown would have become Labour leader had he not messed things up during the campaign. Perhaps Brown was a Soviet spy? (sns at the suggestion).
3. One of Wilson's Foreign Secretaries was a man called Michael Stewart. Without putting too fine a point on it, if Wilson was a Soviet spy he would
not have let someone with Stewart's views anywhere near the Foreign Office.