Since his death in 2010 it has emerged that the former Liberal Democrat MP was a child abuser who escaped justice.
But details of who in 1988 put 29 stone Smith forward to become a “Sir” are shrouded in secrecy.
A document released to the Daily Star Sunday under Freedom of Information laws reveals the grounds for the recommendation.
But the section saying “By whom recommended” is totally blacked out.
According to the Cabinet Office, headed by Sir Jeremy Heywood, releasing the details would breach Data Protection rules. But an MP who has helped expose Smith’s abuse says it should be made public because concerns about him were well known.
In 1970 – 18 years before the knighthood – police sent the then Director of Public Prosecutions, Sir Norman Skelhorn, evidence that Smith had abused eight boys.
But Sir Norman, who died the year Smith was knighted, ruled out charges, saying the allegations were “somewhat stale” and “without corroboration”.
Nine years later, in 1979, two magazines ran details of alleged abuse by Smith but the obese politician – by then a senior Liberal MP – threatened to sue and the case went quiet.