According to my references, this item was produced pre-war and then reissued after the war, being renumbered in 1954, and then continuing until 1962.
In the March 1956 issue of Meccano Magazine, the Toyman has arranged a scene to show off the delights of the new GPO Telephones van. However, he has made a telephone box out of cardboard (not a bad effort), and even suggests that if readers have "the necessary skill and patience" they could glaze their cardboard kiosk with cellophane. Surely he wouldn't have needed to do this if the Dinky Toys model was available - not to mention the opportunity to plug sales.
Therefore, was this item not available at the time? There is a note in the Great Book of Dinky about the telephone box being available only in the USA and Canada in 1954 - perhaps this stayed the case for a longer period? Quite why a UK phone box would only be for export I don't know!
Does anyone have more information to solve this little puzzle?