Have look at the BHS website there are some listed here. If you say where about in Yorkshire are you and what type of instruction do you want you'll probably get a lot of recommendations from folks on here.
The BHS register of instructors. All there instructors hold a minimum of the Preliminary Teaching Certificate, are first aiders, have done a child protection course, and have insurance.
I'm near Castleford in Leeds.
I want a instructor who will teach me mainly schooling, I feel as though I've gone really down hill, and need to have lessons to get me back where I was before.
I'm not going to be competing any time soon so I don't need a top level instructor
It's often good to ask around for recommendations for instructors. If you don't have friends currently having lessons, ask at your saddlers or feed merchants. Sometimes instructors will advertise on their notice boards too. Don't be put off if you don't 'click' with an instructor. There are lots of good ones about, you just have to find the right one for you!
If you have transport, Damien Midgley in Sherburn in Elmet is very good. I also know several people who have enjoyed lessons with the Seniors at Manor Grange.
I train with Tracy Garside who is fantastic but not sure whether she travels over your way.
Good luck! Nice to feel inspired for the new year
The BHS, BSJA and BE will all have a list of accredited trainers. However because people are doesnt meant that they are any good or you will get on with them. Best to do what has been suggested and ask around and go off a personal recommendation.