Table 2.

Key findings from interviews with ACT therapists regarding ACT training and delivery

Fidelity dimension		Key findings
Fidelity of training	Likes	Therapists reported the training was helpful in preparing for delivery of the ACT sessions. Aspects reported as helpful were: - Experiential aspects, e.g. role plays. - Focus on the relational/ conversational aspects to improve psychological flexibility. - Mixture of teaching, interactive exercises, and opportunity for questions.
	Dislikes	One therapist felt the training was slightly too theoretical, which they felt was less necessary when delivering guided self-help.
	Suggestions for improvement	- More training on the trial elements of intervention delivery, e.g. paperwork. - More people in the training to learn from others. - Face-to-face training to improve concentration.
Fidelity of delivery	Self-efficacy of delivery	- Therapists felt confident in delivering the ACT component, which was helped with a therapist training manual to refer to, and opportunity for supervision.
	Manualized therapy	- Two therapists felt the sessions initially felt clunky to deliver due to the manualized element differing from normal clinical practice, but over time they got used to it with familiarity. - One therapist reported difficulty knowing how much deviation from the manual was appropriate.
	Length of sessions	- First session felt too short (15 min)—not enough time to understand the participant’s situation, distress and to explain ACT. - More preparation time needed for the sessions, as it was less familiar. - One therapist felt the sessions were a good amount of time to contain the participant.
	Delivery in context of NHS	- Difficulty working out who would have the time to deliver the intervention within stretched NHS resources. - Some therapists felt assistant psychologists (APs)/psychological well-being practitioners (PWPs) would be more suited to deliver guided self-help. Other therapists had concerns that APs and PWPs would not have the clinical autonomy and experience to deliver the fast-paced intervention, for example, they may struggle with the integrating psychological flexibility into conversation.
	Therapeutic relationship	- Most therapists felt there was enough time within the sessions to build a therapeutic relationship with the participant. - Therapists acknowledged the therapeutic relationship would have been more difficult to build within the time of the sessions in the participants had been more distressed. - More difficulty building rapport via phone call. - One therapist acknowledged difficulty in building a therapeutic relationship due to the teacher/pupil dynamic that can be created in guided self-help interventions. - More time in the sessions (e.g. all 25-min sessions) and more information about the participant prior to the sessions was suggested to improve the therapeutic relationship.