Inclusion Criteria:

• Patients must have a confirmed diagnosis of multiple sclerosis and at randomisation have entered the secondary progressive stage. Steady progression rather than relapse must be the major cause of increasing disability in the preceding 2 years. Progression can be evident from either an increase of at least one point on the EDSS or clinical documentation of increasing disability.
• EDSS 4.0 - 6.5 inclusive
• Women of childbearing age will be required to use appropriate methods of contraception to avoid the unlikely teratogenic effects of simvastatin.
• Able to give written informed consent
• 18 - 65 years

Exclusion Criteria:

• Unable to give informed consent
• Primary progressive MS
• Those that have experienced a relapse or have been treated with steroids (both i.v. and oral) within 3 months of the screening visit. These patients may undergo a further screening visit once the 3 month window has expired and may be included if no steroid treatment has been administered in the intervening period.
• Patient is already taking or is anticipated to be taking a statin.
• Any medications that unfavourably interact with statins: fibrates, nicotinic acid, cyclosporine, azole anti-fungal preparations, macrolideantibiotics, protease inhibitors, nefazodone, verapamil, amiodarone, large amounts of grapefruit juice or alcohol abuse.
• The use of immunosuppressants (e.g. azathioprine, methotrexate, cyclosporine) or disease modifying treatments (avonex, rebif, betaferon, glatiramer) within the previous 6 months.
• The use of mitoxantrone if treated within the last 12 months.
• If the patient has ever been treated with alemtuzumab.
• If screening levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) or creatine kinase (CK) are three times the upper limit of normal patients should be excluded.
• Patient unable to tolerate baseline scan or scan not of adequate quality for analysis (e.g. too much movement artefact).
• If a female patient is pregnant or breast feeding