Somebody put up a picture of one in Essex a short while back on the Yahoo group. I'll try and find it, as I'm not sure when exactly it was taken.
EDIT: it's an old photo, but here it is:
Yes, that's them!
That is amazing to see! Thank you for posting it. I haven't seen these for 30 years (since I was five years old). So it definitely was the elusive P149!
In the 1970s, the B roads around Frinton on Sea, Walton On The Naze and the surrounding villages (Kirby Cross, Lower Kirby, Kirby Le Soken) all used to be lit with the same group B side-entry mercury lanterns on concrete 'hockey stick' columns.This photo was taken in Kirby Road, Walton On The Naze. The date of the photo is 1967, which is about 13 years before the P149s were removed, but most of the the Concrete Utilities hockey-stick style columns like in this picture are still in Frinton, Walton and the surrounding villages today,
albeit with Thorn Beta 5s. Furthermore, the style of the road signs certainly hasn't changed in the last 43 years.
The name Putmans is easily recognised in my corner of Essex. They are a long-established and well-known photography company in Walton On The Naze, and probably took many of my school photos.
Thank you again for posting this photo. I can't quite believe this lantern is now identified, or how good my memory for street lighting was when I was five!