The Group uses foreign currency forward contracts in the management of its exchange rate exposures. The contracts are primarily denominated in the currencies of the Group's principal markets. The unrecognised gains and losses were not material in either 2018 or 2017.

The following summarises the aggregate notional amount (aggregate face value) of all open contracts and their related fair values as of the balance sheet date:

or notional
Fair valueContractual
or notional
Fair value
Fair value hedges
Currency forward foreign exchange contracts0.93.0

In accordance with IFRS 7 Financial Instruments: Disclosures, the Group's financial instruments are considered to be classified as level 2 instruments. Fair value measurements are those derived from inputs other than quoted prices included within level 1 that are observable for the asset or liability, either directly (i.e. as prices) or indirectly (i.e. derived from prices).

Fair value is determined using quoted forward exchange rates and yield curves derived from quoted interest rates matching maturities of the contracts.

The Group's interest rate risk is primarily in relation to its fixed rate borrowings (fair value risk) and floating rate borrowings (cash flow risk). From time to time the Group will use interest rate derivative contracts to manage its exposure to interest rate movements within Group policy. However, at the balance sheet date, the Group had no interest rate derivative contracts (2017: nil).

All forward foreign exchange contracts are on demand or due within one year.