I had a real hard time finding a job in my area that took trainees. I think my employer was super desperate for someone so took me on and sorted out a blended learning course at Bristol Dental Hospital. I had to go there one full day a month for theory. The idea is that all the practical side is taught at the practice. The course lasted 1 year. We have 2 trainees at work now, one is going to the dental hospital like I did, and the other one is learning online with AGEvolution. She seems to be getting along ok with the online course.
Some bigger practices offer their own in-house training. It's best to go on the NEBDN website and look at a list of approved learning providers for the national diploma. You will see all the places near you that offer the training. If you leave near a Dental Hospital, these also offer training and employment for dental nurses. It can be hard to get into though because they only take on a handful of trainees each year. This is what I looked at doing because I was finding it so hard to get a job as a trainee dental nurse.
Harriet Ellis take your money and take you on BEFORE you find a job. You cannot complete the NEBDN without working in a dental environment. So if you go down the Harriet Ellis route and can't find a job then you're stuffed.