If you qualify there are lots of posts. Check the NHS jobs website and type in "High intensity therapist" and see the results.
The trickier part is getting there. The recognised core professions are ones like occupational therapy, mental health nursing or clinical psychology, which all have their pros and cons. Making the jump from a low intensity therapist to high is far harder (because of the lack of core profession).
It may be worth contacting your local IAPT service to talk to the LI staff to see how they are getting on with that. Very few tend to want to stay as PWPs, so there is that bottleneck to making the leap upwards.