It was planted in the autumn 3 years ago & seems to be flourishing but its never flowered
You can check on your plant's growing conditions based on the tips in this article:
https://www.gardeningknowhow.com/ornamental/shrubs/mahonia/grape-holly-plant-care.htm
I'm not clear about your location, but the Oregon grape is native to Oregon where the soil is rich and moist. Your soil's pH should be between 5 and 8, so you may want to do a soil test. https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
Hi, My Oak Leaf Hollies are covered with something that I can't identify. See pic. Additionally, my new growth leaves are turning black and dying. Related? Someone said it's residual material from the new growth. Someone else said it's caused by Bacterial Blight. And yet another person said it's new growth that was killed by an overnight frost. Can you tell me what is really happening?
Did you have some late freezes because it does look like frost damage. If not, here are some common diseases of hollies:
https://www.gardeningknowhow.com/ornamental/shrubs/holly/oak-leaf-holly-information.htm
https://www.gardeningknowhow.com/ornamental/shrubs/holly/diseases-of-holly-bushes-pests-and-diseases-damaging-holly-bushes.htm
Found in garden in Bristol
That is a type of Mahonia! Here are some articles that will help: