Primary sclerosing cholangitis is a progressive immune mediated biliary disease characterised by bile duct inflammation and fibrosis, and accompanying hepatic fibrosis. For patients with elevated alkaline phosphatase (ALP) in particular, progressive disease is predicted, that currently results in a need for liver transplantation in the majority. No current medical therapy has as yet been shown to be effective in altering the natural history of disease. For this reason patients with PSC with elevated ALP values will be recruited to this study, to evaluate the impact of Vap-1 blockade by BTT1023, in an early phase study focused on biochemical efficacy and safety.