Hi,
Its probably an early "Bsa Air Rifle" dating from around 1914/15. Apart from the foresight, which has either been broken off or is a replacement, it looks nice, but it has been refinished which effects its desirabilty and hence value to some but not all collectors.
Its probably worth about £150 to £180 or so, depending on the quality of the refinish, mechanical condition prior to the reblue, whether the cylinder markings are still present, evidence of pitting still remaining under the reblue, any cracks to woodwork, damage etc.
You need some close up pics for a proper evaluation.
Probably be priced at a lot more £'s if you are buying it from a dealer, though.
"helplessly they stare at his tracks......."