We will ask participants to complete the psychological impact of MS scale, anxiety/depression questionnaires and visual analogue scales once a week throughout their involvement in the study (estimated to be 9 weeks). The baseline will be established over a period of the first three weeks (before participants start the intervention). Participants will also be asked to complete a second set of questionnaires (secondary measures) before starting the intervention, to assess quality of life, stress, the impact of MS, MS-related self-efficacy and fatigue.

Participants will then be invited to an optional semi-structured, feedback interview to provide qualitative information on their experience of the intervention.

Participants will then commence the intervention for the next 4 weeks. They will be sent the workbook via post. This will not be a standalone self-help intervention; participants will progress through the workbook alongside weekly emotional support sessions. These will either be over the phone or using an online video-call software, depending on participants preference. The first session will be an hour long to set-up the workbook, answer questions and go through goal setting. The following three weekly sessions will be half an hour to revisit exercises in the workbook, answer questions and review how the workbook progress is going. All sessions will be delivered by a trainee clinical psychologist who will receive standardised training and ongoing supervision from an experienced clinical psychologist.

The principle primary outcome (main primary outcome of interest). Multiple Sclerosis Impact Scale-Psychological Subscale (MSIS-29-PSYCH; Hobart et al., 2001; Ramp et al., 2009). Total scores range from 0-45, with higher scores indicating greater perceived psychological impact of MS. Nine scaled questions with scale values ranging from 1-5.

Change in the level of depression symptoms. Higher scores indicate a worse outcome, total scores range from 0-27, scale values range from 0-3.

Change in the level of anxiety symptoms. Higher scores indicate a worse outcome, total scores range from 0-21, scale values range from 0-3.

Change in (1) the level of psychological distress related to receiving an MS diagnosis, (2) confidence in managing the physical impact day to day and (3) confidence in managing the psychological impact day to day. Scale ranges from 0-10.

EQ-5D-5L (Herdman et al., 2011). Five scaled questions assessing five domains of quality of life (mobility, self-care, usual activities, pain/discomfort, anxiety/depression. Each response corresponds to a 1-digit number. The total responses are combined into a 5-digit number to represent health state, e.g., 11111 represents no problems in health state. These are then converted to an index score; higher scores indicate greater health related quality of life.

Process measure. Scale to measure change in ACT-process of psychological flexibility. Higher scores indicate a better outcome, total scores range from 0-48, scale values range from 0-6.