If I remember right, Alderman is an 'improved' version of Telephone. You can get Alderman from quite a few suppliers, Telephone from Real Seeds, and Ne plus Ultra from Robinsons'. I also grew Purple-Podded from Robinsons' this year, along with Magnum Bonum, and I've added Lancashire Lad and Salmon-Flowered for next year. All the peas I grew this year were a great success. As you can tell, I like these peas, as the crops are so much heavier than what the wretched modern things produce.
The sweet peas we're used to today only came in in Victorian times, and the older varieties (Purple Podded, Lancashire Lad, which is another purple podded one, and Salmon-Flowered) aren't very nice to eat raw. Unless you want to have a little pile of peas on the side of your plate though, it really doesn't matter. We never cook like that.