Suddenly they’re all at it. Actors, that is, writing plays. David Haig, Rory Kinnear and Simon Paisley Day are all poised to offer new dramas to the public. But someone else has got there first. You may have spotted Phoebe Waller-Bridge playing a secretarial cameo in The Iron Lady. She’s a rangy Home Countries brunette with rosy lips, large inviting eyes and an angular, forthright face that suggests intelligence, amusement and a hint of subversive sexual power.