On 17 May 2016, Ted Persons in Maryland, USA wrote:
"I found a British Number Plate (tall variety) in an antique store in Manteo, NC which I mounted to the rear of the car. The lamp bracket is adjustable and gives me enough height. My state plate is mounted below the bumper. -- Can anyone in England perhaps tell me the source for QS as the code? From what I found on the web, Q was used for cars of indeterminate age or perhaps temporary registration? The owners emigrated here back in the early '80s. I'm trying to track them down and find out more about the plate's source".
"I'm also curious as to the style of plate. I've seen this style on MG TD's and others in pictures, but for the most part, over here we see the long narrow variety. Was this an option for the taller squarish variant on the rear? It measures 9 x 12 inches in round numbers.

Malcolm Asquith in Stockport, UK replied:
"The Q registrations issued nowadays are in the format Q 123 ABC and are used for cars where the registration year cannot be determined such as kit cars made up from parts from several years.
"Your number QS 1728 predates this and is part of a series issued in London to cars that were temporary imports. I'm not sure how long a car had to be in the UK to need one nor do I know when they stopped using the system but I suspect it was around 1964 when the system changed to allow a max of 7 digits rather than the previous six to be used. The list I have looked at was dated 1955 so they were in use then".

Malcolm Asquith in Stockport, UK wrote:
"Number plates can be either the long or squarish type, but in recent times the square ones seem to be a dying breed. The square ones were common on the rear, but there is no legal reason they cannot be used on the front, but this is rare. -- This was the caption on a website photo I found":
"The ‘Q’ series had a long history in Britain, starting in 1921. Another use for them was to temporarily register a visiting car from a country which did not subscribe to the international conventions. Thus they were unable to circulate using their foreign registration plates. This vehicle entered GB for a rally in 1932, and the Automobile Association issued it this QE 475 tag for the duration. The AA and the RAC were authorized to allocate these plates on behalf of the State, to facilitate motor tourism, as all the complex services were offered by those two venerable Clubs".
"A further note on another photo says QK was in use in 1964. -- In 1983 the format was reversed putting the letters after the numbers so that gives a last possible date for your number. QS was issued by the RAC (Royal Automobile Club)".

Steve Gyles in Hampshire, UK wrote:
"Back in 1972 I was flying with the RAF in Germany. I came back to the UK to pick up my brand new duty free car to take back to Germany. I was issued with QM 6532. This allowed me to use the car in the UK for up to 6 months (if necessary) before exporting it abroad. I then had to keep it overseas for a minimum of 12 months before bringing it back (permanently) to the UK to avoid all the purchase taxes, etc. When I did return permanently I was issued with the current registration number AUR 107N (1974), being the first date of registration in the UK. The Q plates were very common in those days with thousands upon thousands of military personnel doing the same thing".