The NHS was the result of a process started in 1942 and was completed in 1948. It was a Liberal idea that stemmed from the Beveridge Report of 1942. If anyone was the architect of the NHS it was Beveridge, NOT Bevan.The white paper that paved the way for the foundation of the NHS was prepared by a Conservative Minister for Health, Henry Willink in 1944.
All the necessary legislation required to permit its founding, except for the final bill, was passed before the National Government, led by Churchill, left office on July 5th 1945.
Particularly important was the financial and enabling legislation that allowed privately owned assets to be passed into state ownership.
When the final Bill that created a National Health Service as a legal entity was put before Parliament by Bevan, the Minister for Health, in 1946, all the important spadework had already been done.
The NHS was on its way regardless of which party won the 1945 election, so for Labour to claim full credit is akin to the anchor man in a relay team claiming credit for the whole team's victory.