What was the first British trade paperback?

So, here's a question I don't know the answer to but I thought it might be interesting to turn it over to the hive mind and see if we can come up with an answer...Which was the first British "trade paperback" to be published? I know this (US) definition is usually applied to volumes that typically reprint 4-6 issues of any given title.

I'm differentiating it from the term 'graphic novel' which I'm taking to mean a title published entirely as one volume. Whatever.

I'll open the bidding with this item, this is an overs-sized (and extremely flimsy) softback reprinting of the (original) Eagle magazine back-page strip The Baden-Powell story. It appeared in 1957 and had originally appeared in Eagle volume 5 number 17 (23/04/54) to volume 5 number 45 (05/11/54), written by Geoffrey Bond (under his Alan Jason pseudonym) and is illustrated by Norman Williams.