It will only dent cans and is very inaccurate. Can I get it serviced and are spare parts still available?
Your air rifle is a Mark 2 Airsporter. This was a very accurate and powerful air rifle and, with the Webley Mark 3 underlever, was the joint market leader of its day.
As it has been stored for so long, I suspect that the leather piston washer has dried out and lubricating grease has long since evaporated from the piston and mainspring.
I would suggest that you fill the breech plug with leather oil, or any non-mineral lubricating oil such as animal or vegetable oil, and work the cocking lever a few times to draw the oil into the cylinder where it will soak into the piston washer and nourish the leather.
Fire a few pellets and you will probably find that it is now working well.
If this doesn?t work, then the piston washer may need replacing and you will have to strip the rifle and fit a new piston washer, spacing washer and nylon retaining cone.
Trim the washer so that it is an easy fit in the cylinder and re-lubricate with leather oil.
As to accuracy, are you using the correct size of pellet?
Your rifle is a true .22 calibre and fires 5.5mm pellets, whereas modern air rifles fire 5.6mm pellets.
The old size pellets are still available from most good gunshops.