You may be right, Stimpy. My source of data is the book "The House of Horror", the complete story of Hammer Films, and that lists Jekyll as being released in 1960.
However, the British and US release years were often different, so the movie may have come out in America the following year. If you check out the official Hammer web site -
www.hammerfilms.com - the film is not listed as having been produced in either 60 or 61, so who knows?!
I'm very proud to have met Mr Lee, one of my all time heroes. You may be interested to know that before I was introduced to him his agent told me not to ask him about Hammer, as apparently he "doesn't like talking about the old Hammer days". Luckily for me he mentioned Hammer of his own accord almost immediately, then spent an hour reminiscing on the subject!!