I've got A Distant Mirror, but lke so many others on my shelves I've not read it.
York is a lovely city; I'm about 90 miles away, Major 80. One of those places that has a visible history going back to the Romans nearly 2000 years ago.

On the subject of herbal medicines (nature has the answer to every question on earth, whether it be science, engineering or medicine etc) When I first moved to my present home in 85, I had a neighbour who was 90 at the time. He was a fascinating, multi talented man, who had lived in this village all his life. You can just imagine how different things were when he was a child and his mother was the village doctor, so to speak. People came to her for her herbal medicines, because she was free, they couldn't afford a doctor. He was an ex army man and he didn't walk, he marched up the lane every day and on his way back, he sometimes had some plant life in his hand. I used to chat to him regularly and so asked him about what he was doing and it turned out he was making his own medicines, as he was taught to by his mother. Now here's the strange thing. His neighbour was somebody he grew up with and she knew all about him and his mother. The poor old dear had a wound on her leg, which refused to heal. She was visiting the hospital regularly and they were treating her. In the end she went to see her old neighbour and he mixed her up some poultice or other and it worked. He told her before he treated her not to tell anybody and me not to tell anybody because, as he said, I don't want every nutter and his brother knocking on my door to be cured. These things are lost now.

 I've been to York a number of times, it's a very interesting city, with a strong Viking inheritance. York Cathedral is wonderful.

That old lady sounds like one of the last Lancashire witches.

The Guilds in Shula's novel became powerful about the time the story is set, in the middle of the 14th century under Edward III. When a town became a Borough it was usually granted the right to form a merchant guild controlling trade within its boundaries and limit the number of outsiders who wished to become traders there. They evolved into craftsmen's guilds which still exist today but without the powers they once had.

The Duke of Lancaster in Question is, I assume, Henry who died (along with his wife) of the plague in 1361. 

You could probably buy the full Cadfael series as one set from Amazon. I used to read them at intervals as if I read one after the other I got the characters and plots mixed up.
They were dramatized first on the radio and then on TV with Derek Jacobi in the TV version. 

 There is a Shambles in Manchester, which has a very interesting story. At it's centre is the pub and it dates back to the 1552. However, it's not where it used to be, as they jacked it up and moved the entire building to a new site. The area was originally a butchers area and blood and guts would have been running down the streets, hence the term has survived as meaning a mess.

I did as you suggested, Mark, and it looks a lovely, quaint place to visit.  I love the little shops.  I hadn't dared hope it still existed.

 There are a few pubs in Stratford Upon Avon that are around the 500 year old mark, Mark.

 You must have tried Little Moreton Hall Mark, it's in your patch

Is there supposed to be a picture, there's nothing there, or is it just me.

 I've just tried it and the video worked for me.

Just a blank space. What can Shula see?

Drat.  I can't see the video either.