13 Deferred tax

Deferred tax assets comprise:

Deferred tax liabilities comprise:

The net deferred tax liabilities / (assets) are reflected in the balance sheet as follows, after offsetting assets and liabilities where there is a legally enforceable right to offset current tax assets and liabilities and where the deferred income taxes relate to the same fiscal authority.

Deferred tax expected to be recovered within 12 months:

At the balance sheet date, the Group has recognised and unrecognised deferred tax assets in respect of unused tax losses of £144 million (2005: £137 million) available for offset against future profits. A deferred tax asset has been recognised in respect of £32 million (2005: £18 million) of such losses, as realisation of the related tax benefit is probable.

Unrecognised deferred tax assets in respect of unused income tax losses of £67 million (2005: £69 million) have no expiry date and unused income tax losses of £35 million (2005: £40 million) expire after 5 years. Unrecognised deferred tax assets in respect of unused capital tax losses of £10 million (2005: £10 million) have no expiry date.

At the balance sheet date, the Group has unrecognised deferred tax assets in respect of deductible temporary differences of £183 million (2005: £179 million) and unused tax credits of £136 million (2005: £133 million). £nil million (2005: £10 million) of these unrecognised deferred tax assets expire after 5 years, whilst the remainder have no expiry period.

At the balance sheet date, the aggregate amount of temporary differences associated with undistributed earnings of subsidiaries for which deferred tax liabilities have not been recognised was £5 billion (2005: £5 billion). No liability has been recognised in respect of these differences because the Group is in a position to control the timing of the reversal of the temporary differences and it is probable that such differences will not reverse in the foreseeable future.

 14 Trade and other receivables

Impairment on trade receivables charged in the year as part of other operating expenses was £17 million (2005: £7 million).

Prepayments and accrued income include £48 million (2005: £45 million) in respect of dividends from associates and £1 million (2005: £1 million) in respect of interest.

Trade and other receivables are predominantly denominated in the functional currencies of subsidiary undertakings apart from the following:

Trade and other receivables also include certain interest bearing amounts and their effective interest rates as follows:

*Includes US$100 million (£51 million) (2005: £58 million) representing a bond posted in connection with the Engle class action in the US (note 30).

There is no material difference between the above amounts for trade and other receivables and their fair value, due to the short term duration of the majority of trade and other receivables. There is no concentration of credit risk with respect to trade receivables as the Group has a large number of customers, internationally dispersed.

 15 Available-for-sale investments

Investments have the following maturities:

Investments are denominated in the functional currency of the subsidiary undertaking or other currencies as shown below:

Non-equity investments are denominated in the following currencies:

Effective interest rates applicable to non-equity investments are as follows: