Welcome to the forum Andy.
What a cracking find. There were around 1500 of these rifles made during the latter 1920s and they are quite desirable today.
There is an excellent section on them in Chris Thrale's book Webley Air Rifles and Chris also lists the serial numbers of all known examples. Yours is not among them and is therefore a 'fresh' example in collecting circles.
Enjoy - these are lovely little rifles. I would rectify any mechanical deficiencies sympathetically and not touch the external finish beyond a good oiling or waxing as refinishing would devalue such a nice historical item.
John