The Brit 28 you're most likely to run across would be one from Webley & Scott's Model 700 series. They are modern guns, all made after WWII. 28ga 700's were not made until 1966. There was also a Model 728, which is basically a Model 702 (which is the middle of 3 grades in the 700 series) in 28 ga. But I believe all of those were made with 26" barrels. As Brit 28's go, they're relatively numerous.