The overall aims of the study are:

Aim 1: Estimate effect sizes: To estimate the effects of dCBT-I on insomnia symptoms compared to a control group (sleep hygiene education) and estimate the relationship between changes in insomnia symptoms and the reduction in migraines.

Aim 2: Explore mechanisms of change: To explore the mechanisms underlining the change in migraine symptoms.

Aim 3: Assess barriers to conducting a full-scale RCT: To collect data on recruitment pace and dropouts in both groups, which will help refine the methodology and maximise uptake and retention of a full-scale randomised control trial (RCT). The investigators will conduct qualitative interviews with a select number of participants and practitioners to identify motivators/barriers in uptake of a digitalised version of CBT-I.

Chronic migraine (CM) is a debilitating condition that places a direct burden worth £150 million on the NHS per year. Previous research has shown that insomnia is a risk factor for migraines. The investigators hypothesise that two modifiable behaviours explain this relationship between insomnia and migraines: daytime napping and nocturnal light exposure. To cope with the migraines, individuals will nap during the day, reducing the homeostatic drive for sleep at night and delaying sleep onset. This inability to fall asleep potentially increases exposure to evening bright light, delaying the release of the hormone melatonin and reducing sleep quality. Poor sleep in turn is a trigger for migraines, which creates a vicious cycle of migraines and poor sleep. The investigators believe that these behavioural mechanisms are valid targets for treatment and are explicitly addressed in Cognitive Behaviour Therapy for insomnia (CBT-I). Digital versions of CBT-I (dCBT-I) offer a scalable solution to the problem of limited access to CBT-I. This research group has demonstrated the feasibility, acceptability and preliminary efficacy of dCBT-I in an uncontrolled proof-of concept study. Utilising randomised control trial (RCT) methodology, the investigator's aim now is to evaluate the effectiveness of dCBT-I for improving insomnia and migraines in patients with chronic migraines. The second aim is to probe mechanism of change and to test the hypotheses that behavioural markers such as daytime napping and evening light exposure can reduce insomnia symptoms leading to an improvement in migraines. Prior to progressing to a full-scale RCT, the investigators require a feasibility RCT, to refine the methodology. The investigators propose to recruit individuals who meet criteria for CM and insomnia, directly referred from two neurology clinics, who will act as clinical recruiters. Eighty-eight participants will be randomised either to a dCBT-I group or to sleep hygiene education (SHE) control group. The main outcomes are insomnia and migraine days and will be collected at post-treatment, and long-term effects will be assessed at month 6.

Inclusion Criteria:

1. Women age 18 and above
2. Insomnia, satisfied by a total score ≥ 11 on the insomnia severity index (ISI)
3. Headache ≥ 15 days per month, ≥ 12 months and meet criteria for migraine with/without aura on ≥ 8 days per month, ≥ 12 months

Exclusion Criteria:

1. Medical condition that is unstable, requires immediate treatment, or is judged to interfere with the protocol, including other pain conditions such as chronic low back pain and fibromyalgia and also sleep disorders such as untreated sleep apnoea or parasomnias.
2. Psychiatric condition that is judged to interfere with the study protocol including substance abuse, psychotic disorder, cognitive disorder, current suicidal ideation, or any uncontrolled psychiatric conditions that require immediate treatment
3. Regular use of illegal substances
4. Women who are pregnant or breastfeeding
5. Shiftworkers

While the study will be single-blinded (researchers analysing data will be blind to allocation), randomisation will be concealed to the RA and participant until the individual's eligibility has been established.