Experience of Point-of-Care HbA1c testing in the English National Health Service Diabetes Prevention Programme: an observational study by Barron, E, Misra, S, English, E, Barry, WG, Sampson, M, Bachmann, MO, Barth, J, Oliver, N, Alberti, KGMM, Bakhai, C, O'Neill, S, Young, B, Wareham, NJ, Khunti, K, Jebb, S, Smith, J, Valabhji, J