I took another look. IMHO various houses were built with integral garages. They have a similar floorprint, only some details at the front differ.
At a later time, the entire street went for double glazing and low maintenance plastic. They also replaced the garage doors. Did they hide the original front doors (except one that I can see) behind a new outer entrance? Or was this part of the original construction? A few houses have a flat roof over the extension.
You can still see front doors through the windows.
Being so near to the sea, this makes sense.
There is one house up the street that kept the original garage doors. Look at the black hinges. They also went to great lengths and cost to preserve the stained glass windows, these were integrated in the double glazing (with exception of the new entrance obviously).
This is the house:
View attachment 268843
IMHO (repeat button), the garage was part of the original construction. The rumour that the Clarks built it to hide something underneath the floor is bogus.