What is a shirt-sleeve pudding and why is it so named?

Shirt sleeve pudding

So called because apparently it was steamed in an old shirt sleeve, this is jam roly poly by another name. To most people the idea of steaming anything for up to three hours is way too big an ask. Nowadays people are more likely to stick a homemade JRP in the oven but it does beg the crucial question: to steam or to bake? According to Peter Henderson, Chairman of The Pudding Club, it's down to whether you fancy yours moist or crusty. A variation is granny's leg, studded with raisins to conjure up an image of an aged warty limb. Make mine a large slice.
http://www.channel4.com/food/features/top-10s/top-10-old-school-British-puds_p_1.html

Here's a recipe:
http://www.channel4.com/food/recipes/popular-cuisines/british/shirt-sleeve-pudding-recipe-jam-roly-poly-08-09-25_p_1.html