We would call that keeper's tweed, but it's a slightly lighter weight than is usually seen on a riding coat. My own is 35 oz and it's definitely thornproof - I posted a photo of it here
some time ago.
The coat shown is cut for riding, obviously, and as such would usually have a panel back, but for some reason does not.
Harry Hall has been well known here for decades but I had been under the impression the firm had for some time confined itself to the bottom end of the ready to wear equestrian market. Perhaps I was mistaken.
"Ratcatcher", by the way, simply means less formal hunting wear, as worn for autumn hunting ahead of the opening meet, and while a coat in keeper's tweed, worn with a coloured stock and brown boots, is the most common interpretation, a coat of almost any tweed might be worn. In an attempt to tone things down, some hunts in England now wear ratcatcher throughout the season.