Strawbs' greatest hit, originally recorded by John and Hud (with some help from Blue and Lambert) and intended for release under the name of "The Brothers", it was included on Bursting At The Seams instead, and pulled for release on 45 by the record company. Dave Cousins would have preferred to release "Stormy Down" as the second single, but "POTU" was the record company choice, and, finding its moment in the industrial unrest of the early 70s, it stormed up the UK charts to reach number 2.
The intention in choosing a traditional song (from the Strawberry Hill Boys' old repertoire, was that all the band members would get a share of the publishing royalties on the B-side. Unfortunately "Will You Go" is not in fact traditional, but was written by the famous McPeake family. Oops! IT's still a great track, not released on album until UK Halcyon Days CD; it also appears as one of the bonus tracks on the re-issue of BATS. It was always a great crowd pleaser on the '73 tour, with Blue strapping on the accordian and coming up front to pose with Dave C; its return at Chiswick '98 and on the '99 tour was most welcome indeed.
The promo release is dated 4 Jan 1973.
Sonet, Strawbs' original record label, released both "Lay Down" and "Part Of The Union" in really attractive picture sleeves.
A strange pairing of tracks, the faintly frivolous matched with the bitter and twisted.
However, the real treasure from the US is a promo only 10-inch single version, complete with lavish foldout cover.

Front and back covers

first foldout

fully opened out
Canada put "Tomorrow" on the B-side. There was also a stereo/mono promo release. Both sets of scans from Alison Brown. Note that the single wasn't released until later in the year in order to coincide with Strawbs 1973 tour in North America.
A fairly tatty sleeve in dull green, yellow and black, the band vignette photos pulled (I think) from an issue of Melody Maker.
A Roy Lichtenstein inspired cartoon fist "adorns" this German release. Though both copies I have are in the same sleeve, one copy has "New World" as the B-side. If you can read anything into the matrix numbering (those numbers in the run-out groove of the record itself):
POTU - A4
Will You Go - B3
POTU - A5
New World - B7
it seems possible that the "Will You Go" release was the earlier. But I'm guessing ...
Garish orange, featuring the "tweed" photos. The rear cover notes the single's achievement in the unofficial NME chart in the UK (where it got to number 1) and advertises "Lay Down". "Part Of The Union" was obviously untranslateable ....
The fist motif a popular one, it also resurfaces on the French release.
The Italians backed the single with "Lay Down" which they must have missed out on first time round, and lifted the five piece design from the cover of the album Bursting At The Seams. The printed cover gives a date of 1972, which must be spurious as POTU wasn't released until early 1973.
The "goldfish bowl shot, also used for the Spanish version of "Lay Down", the Japanese picked "Heavy Disguise" to back the release. Wonder what they made of our boys' union frolics ....
Another gloriously anachronistic photo, again of the Antiques & Curios team, all kaftans and duffel coats, and NOT the glam-rock ensemble that they had transformed themselves into by this stage.
Portuguese sleeve scans by Alison Brown
These Polish flexi-discs have to be the strangest Strawbs 45s. The surface is clear plastic and the details only show up against the light.
The first one looks like a piece of Granny's wallpaper and the band name is mis-spelled as "The Stawbs". The whole of the track is played on the second disc which has a more appealing tree and cockerel design.
A straightforward picture sleeve or a Turkish EMI company sleeve for this release in Turkey.
New Zealand sleeve scans by Alison Brown
Can only presume that the cover featured artists were the Grassroots - certainly not Strawbs, Wizzard or Thin Lizzy who were the other artists on this Thai special, probably a bootleg.