Non-underlying items charged to operating profit comprise:

2018
£m
2017
£m
Amortisation of acquired intangibles
— classified within selling, general and administrative expenses46.129.0
— classified within research and development expenses8.011.4
Impairment of assets available for sale0.6
Remeasurement of contingent consideration(0.1)
Fair value uplift of inventory acquired through business combinations5.14.2
Rationalisation costs0.8
Expenses relating to acquisition activities3.12.1
Rationalisation of manufacturing organisation2.9
65.148.1

Amortisation of acquired intangibles reflects the amortisation of the fair values of future cash flows recognised on acquisition in relation to the identifiable intangible assets acquired.

The remeasurement of the contingent consideration balance relates to the net credit to the income statement on the reassessment of future milestone and royalty payments on a licensing agreement.

The fair value uplift of inventory acquired through business combinations is recognised in accordance with IFRS 3 'Business Combinations' to record the inventory acquired at fair value and its subsequent release into the income statement.

Expenses relating to acquisition activities includes legal and professional fees incurred during the acquisitions of AST Farma and Le Vet (£2.8 million) and Other (£0.3 million). Other is offset with the profit on the sale of human marketing authorisations acquired from previous acquisitions of £0.4 million.

Rationalisation of manufacturing organisation relates to the cost associated with this strategic programme.

Impairment of assets available for sale in the prior year relates to the impairment of the investment in Jaguar Animal Heath Inc.

Rationalisation costs relate to the integration and restructuring programmes implemented subsequent to acquisitions.