Licences, patents, know-how and marketing rights separately acquired or acquired as part of a business combination are amortised over their estimated useful lives, generally not exceeding 20 years, using the straight-line basis, from the time they are available for use. The estimated useful lives for determining the amortisation charge take into account patent lives, where applicable, as well as the value obtained from periods of non-exclusivity. Asset lives are reviewed,
and where appropriate adjusted, annually. Contingent milestone payments are recognised at the point that the contingent event becomes certain. Any development costs incurred by the Group and associated with acquired licences, patents, know-how or marketing rights are written off to the income statement when incurred, unless the criteria for recognition of an internally generated intangible asset are met, usually when a regulatory filing has been made in a major market and approval is considered highly probable.