In June 1967 "the Who" released two Rolling Stones songs (The Last Time and Under My Thumb)as a double A-side single. This was to show their solidarity with Mick and Keith, who had just been given prison sentences as a result of their drugs bust earlier that year. The prison sentences were overturned as you may recall, just as the quickly recorded single was released, partly as a result of public pressure. My question is though, who played bass guitar on this Who single?

It was Pete Townshend, John Entwhistle was on his honeymoon at the time of recording.
http://www.thewho.net/linernotes/MBBB.htm

Very well done, Jenny. The bass part was overdubbed by Peter Townshend, after first checking with bass player John Entwhistle who was on board the QEII (on honeymoon as you correctly say) that it would be OK. Good answer.