Pete recently did an interview on BBC Radio 4 - You and Yours - which investigated a case history of failed cavity wall insulation.
Planning is a complex and constantly changing area of Government policy. The present government has changed direction three times in nearly as many years. Peter is on a Consultations Committee that reviews relevant Government policy drafts, and there has certainly been a lot of activity in the area of Historic Environment. Five years ago, we were still using PPG15 - a time tested system that everyone knew and understood - it had some really good advisory appendices which set out what could and could not be done. It even talked about materials to be used. Then, the current Government decided to make things 'simpler'. Along came PPS5 - which was certainly shorter - but really wasn't that good at protecting our built heritage. No sooner had we reviewed and requested that the Government re-write PPS5 - which to their credit, they actually did... they sneakily decided to make it EVEN EASIER! So along came the National Planning Policy Framework - the NPPF. It's known amongst conservation folks as the Developer's Charter. If you have a good lawyer, you can probably do almost anything with a Listed Building you want these days.
Certainly the NPPF makes good reading - but I dont think that having read both this and PPS5, you'll be any the wiser about whether what you want to do is legal or not. You are still best to do two things - if your home is Listed, speak to someone who specialises in planning policy first to get some broad help about what you can and can't do - often people's ideas fall into 'You CAN or you CANNOT' categories, so it saves a lot of soul searching further down the line. Once an idea is down on paper and properly researched, you can talk to local Conservation - see the pages we've written on Listed Building Consent...
Peter is very well versed with planning policy - but to give an example of how hard things are, he wanted some years ago to add a timber framed garage to his own home. It has taken several weeks of research to find out whether planning permission is actually needed for it - and his house isn't even listed. Even the Local Authority could not give a 'yes' or 'no' - but it was well covered wtihin the 'permitted development' rights anyway.
The Historic England website also has a lot of information, but it's spread over a lot of categories, and doesnt really look at the practicality of most issues. Certainly worth a read though if you want to get into nitty gritty.