This image (the full size is shown at bottom) printed on the back page of The Eagle showing a cut away drawing of the BT Tower in London (formerly the Post Office Tower) was published in 1964 by the GPO. Its a large sized poster about 1050cm x 650cm which I assume was the size of most small posters used around the country.
The tower on the front of The Eagle 23 May 1964
The Eagle printed the full image on its back page. The front of the paper is shown above with a rather different image of the Tower. The words at the bottom of the page refer to the poster, the sample of which I have printed below.
The Eagle was a tabloid sized paper so the actual image was somewhat small compared to the full version. The full sized poster was available to order by post.
I sent for a copy and eventually received my Post Office Tower poster, rolled in a tube. It is shown below. It was definitely the biggest poster I had ever received as a kid.
Around 1975 I had the poster attached to a cloth backing to make it stronger and more presentable.
The Post Office Tower poster – printed in large for the GPO, May 1964.
This was released in anticipation of the opening of the Post Office Tower. At the time of publication the tower had not even been finished. Topping out took place in July 1964 and it was officially opened 8th October 1965.
This was posted for the 51st anniversary of the tower.
— BT Tower (@bttowerlondon) October 8, 2016
Note: The Swift was a companion paper to the Eagle. It was merged with the Eagle in March 1963.