How do you know when spring has finally sprung? Is it the brighter mornings? The bounty of crocuses and snowdrops sprouting in gardens? Or the new Pret-a-Manger menu? The answer may be all of the above. But if you’re anything like us, you’ll know it’s arrived when you find yourself living in your trench. Before you slip one on, here’s everything you need to know about this transitional weather saviour.