I have a suspicion that this is the 1958 Bomber Command Emergency War Plan; there were 44 targets in 40 cities (more than one target in Moscow and Leningrad, IIRC); the figure of 38 is applicable as this was the estimate of Soviet casualties in millions.
This was referenced in Richard Moore's
Nuclear Illusion, Nuclear Reality.
Edit - clearly the source for some of the info
Nuclear Weapons: An Accident Waiting to Happen - Guardian (about half way down page, but do a find in page search for '44' and it'll get you there.