Looking at the enlarged photo,
The style and the horizontal panel and colour spits are typical of Sprite in the 1960's.
Based on the width of the door opening, divided into the whole length it points to a 10ft model.
Just above the hinge side of the door the picture suggests the roof has a small fold line rather than a continual curve to the profile.
The front window is also quite narrow.
The roof also has a bit of a fold line rather than just a smooth curve
Rooting through Google images I have found this which looks to have the same features Its listed as "Dotty, 1964 sprite 400 vintage, retro caravan". However there are other caravans also listed as 1964 sprite 400's with different roof lines, so I can't be certain about the specific model your interested in.