philmh: yes, exactly - and thanks for the added detailed information. the strange five-digit "W 15551" cat# may've been a pye records creation - with "W 15552" for the separately-issued second lp ?
Hi ppint, Billboard of 14th August 1965 reports the WB-Pye deal as commencing that month, launch party taking place on the 19th and first releases on the 20th, though there's no mention of this release. This album had previously been released through Decca as WM/WS 8158 (copies are in Discogs, which also has this Pye issue as a 1964 release, but that is about to be changed!). I haven't been able to find a specific date for this version, but Gramophone of February 1966 has the group's subsequent album SEE WHAT TOMORROW BRINGS mentioned in a Keith Prowse Music ad, so I would imagine that is the absolute latest that this would have been released, but I tend towards 1965. There doesn't appear to have been any UK 2LP issue.
this uk lp cannot have been released before 1965, else it'd've been pressed & issued by decca with a WM xxxx cat# as a mono lp.
it is prob'ly a 1965 release, but i do not have a definite date for it.
it was a double album in the states: this is just the first two sides - was it released as two single lps by pye, as it was by decca; or as a double album?