(as) plain as Dunstable road

Straightforward and easy to understand. The straight road of Watling Street connects the town of Dunstable, in Bedfordshire, to London. Primarily heard in UK. Why can't you understand I'm saying? I told you as plain as Dunstable road what I meant! These directions are plain as Dunstable road, so you shouldn't have any questions. A: "I'm going to make this plain as Dunstable road. You have to drop the package off by 5 PM sharp so that it will get delivered tomorrow—and it must get delivered tomorrow. Got it?" B: "Yes, sir."