The extended driving test is no different from the standard driving test except that it is longer. So you can learn with any Approved Driving Instructor (ADI) near you live in Bristol. As long as you can show that you are a competent driver who can drive safely, you should have no problems passing the test. The test is longer for drivers who have been disqualified because the court wants to be double sure that you are not going to be a threat to the society when you are allowed behind the wheels again.
If you have any family or friends who can recommend a competent driving instructor in your area, it might be worth going with him than somebody else.