HMRC is not run to make your life easier you know. HMRC is a revenue collection service and is designed to be run with as little outside interference as possible, to ensure the smooth running of the operation. It makes perfect sense that they send you letters without the information for you to...
Over the years, I have become used to poor service and performance from public services. That way, I'm not disappointed when they match my low expectations, which is usually, and on the odd occasion when they exceed expectations, it's a pleasant surprise.