BackgroundSuboptimal glycaemic control in type 2 diabetes (T2D) is common and associated with psychological barriers.AimTo investigate whether it was possible to train practice nurses in six psychological skills (Diabetes-6 [D6]) based on motivational interviewing (MI) and basic cognitive behaviour therapy (CBT), and whether integrating these with diabetes care was associated with improved glycaemic control over 18 months compared with standard care.Design and settingTwo-arm, single-blind, parallel cluster randomised controlled trial in primary care.MethodAdult participants (n = 334) with T2D and persistent HbA1c ≥69.4 mmol/mol were randomised to receive 12 sessions of either the D6 intervention or standard care over 12 months. Practice nurses were trained in the six psychological skills and their competencies were measured by standardised rating scales. Primary outcome was a change in HbA1c level at 18 months from randomisation. Secondary outcomes were changes in systolic and diastolic blood pressure, body mass index, waist circumference, depressive symptoms, harmful alcohol intake, diabetes-specific distress, and cost-effectiveness.ResultsUsing intention-to-treat analysis, there was no significant difference between D6 intervention and standard care in HbA1c (mean difference −0.79 mmol/mol, 95% confidence interval [CI] = −5.75 to 4.18) or for any of the secondary outcomes. The competency level of D6 nurses was below the beginner proficiency level and similar to the standard-care nurses.ConclusionTraining nurses in MI and basic CBT to support self-management did not lead to improvements in glycaemic control or other secondary outcomes in people with T2D at 18 months. It was also unlikely to be cost-effective. Furthermore, the increased contact with standard-care nurses did not improve glycaemic control.