Impairment of fixed assetsA review for indicators of impairment is carried out at each reporting date, with the recoverable amount being estimated where such indicators exist. Where the carrying value exceeds the recoverable amount, the asset is impaired accordingly. Prior impairments are also reviewed for possible reversal at each reporting date.For the purposes of impairment testing, when it is not possible to estimate the recoverable amount of an individual asset, an estimate is made of the recoverable amount of the cash-generating unit to which the asset belongs. The cash-generating unit is the smallest identifiable group of assets that includes the asset and generates cash inflows that largely independent of the cash inflows from other assets or groups of assets.For impairment testing of goodwill, the goodwill acquired in a business combination is, from the acquisition date, allocated to each of the cash-generating units that are expected to benefit from the synergies of the combination, irrespective of whether other assets or liabilities of the company are assigned to those units.Financial instrumentsWhere the contractual obligations of financial instruments (including share capital) are equivalent to a similar debt instrument, those financial instruments are classed as financial liabilities. Financial liabilities are presented as such in the balance sheet. Finance costs and gains or losses relating to financial liabilities are included in the profit and loss account. Finance costs are calculated so as to produce a constant rate of return on the outstanding liability.