From private health web site:
What is the cost of private treatment?
Due to the length and complexity of the treatment, root canal costs can work out quite expensive. Most private dentists start their root canal charges at around £360 per tooth, with the price rising on a sliding scale depending on the number of roots, the difficulty of the treatment, and the number of sessions required. You may also have to pay separately for x-rays, antibiotics, and other peripherals. If you require a cap or crown, this will further increase the cost. Most private root canal bills are in the range £360 to £475 per tooth.