Black Worcester is probably the oldest English pear still in use. It can be traced back to the early 16th century, and is probably much older than that.
Black Worcester pre-dates the trend towards the Continental sweet buttery-fleshed pears that became popular in Victorian England. Instead the flesh remains hard, more like an apple, and is interspersed with gritty flecks. It sounds somewhat off-putting, but don't worry - this is not a pear you eat fresh, but rather one for the kitchen. Slow cooking transforms the fruits, and this is the definitive choice for traditional English stewed pears.
Black Worcester is also quite widely known as the Warden pear, although this is probably an old English term used to describe any long-keeping culinary pear.