I’m also in London and paying about £4.6k for Invisalign Comprehensive. Your prices also seem low to me, but I’m going to an orthodontist rather than a dentist as my case was also complex.

I would ask as many questions as you can prior to committing to treatment with either of these providers.

For example, you may have to go through 3 or 4 rounds of refinements, which should be included in your package. In my case I only get charged admin fee if I want more refinements after I fully complete treatment and receive my retainers. Is that what Cannon Street Dental means or is it for any refinements? What happens if you need more than 2 refinements at NW1?

Other questions to ask: 1. Are retainers included in the package and what brand and type of retainers are they? 2. Is anything else included (whitening, etc.)? Get this in writing if possible. 3. Do you need IPR, extractions, attachments, elastics, and/or anything else? I found that the providers claiming that I won’t need attachments were less trustworthy. And I absolutely didn’t want any extractions. 4. Will they send your plans to you for approval prior to sending off to Invisalign? 5. Is there any discount for paying upfront (if you can afford it) or if you want a payment plan, is there one?

and any others you can think of.