That is a very early variant. First created in 1953, hence LP53. That smooth finish of the receiver, and lighter coloration of the grips ran for 4 yrs until about 57, then replaced by darker brown grips and a crackle finish to the receiver like my 57/58 version...shown here.
That version also had an adjustable trigger pull by means of a small screw down inside the receiver, later dropped on my 57 version, but ironically the trigger pull was much improved for the non adjust model. A 2 stage none adjust trigger of barely 1.5 lbs pull, possibly the best trigger ever fitted to a sporting air pistol. The earlier adjustable pull was still very good, at least as good as a HW45 and twice as good as any Webley air pistol.
They produce approx 400 fps to 420 fps with light match pellets in OEM spec but can be tuned to 500 fps due to a very efficient compression volume, despite the short stroke. I have had as high as 520 fps with 8 grain pellets.
Finally, the stylish beaver tail rear to the receiver was dropped for the less desirable slant back and the brown grips replaced for plain black grips. @1970. It was never as good, with a reduced quality parkerised finish and poor finish to the cylinder.
Once learnt to shoot, the pre 70 versions are very underrated pistols, often winning vintage pistol side shoots and MPL competitions, provided Falcon, or JSB RS pellets are selected.
Piston head seals are often dried out and past repair. I make my own.