Originally Posted by pdurrant
It's certainly out of copyright in the US, as the copyright wasn't renewed. However, it's not out of copyright in the UK.
It was published in 1961. When the copyright wasn't renewed, it fell into the US public domain 28 years later in 1989. However, in 1989 the rule of the shorter term did not apply in the UK, and so it's in copyright in the UK until 70 years after the authors death, and will enter public domain in the UK in 2070.
Oops! I wasn't thinking of the geography angle!