Amounts receivable from related parties including associated undertakings are shown in note 29.

Trade and other receivables have been reported in the balance sheet net of allowances as follows:

The movements in the allowance account are as follows:

Impairment of trade receivables, including write offs and allowances, charged during the year is included as part of other operating expenses. For 2011, the net impairment charged was £11 million (2010: £3 million) of which £8 million (2010: £nil), is reflected in the above table.

As at 31 December 2011, trade and other receivables of £42 million (2010: £58 million) were past their contractual payment date but not impaired. These relate to a number of external parties where there is no expectation of default. The aged analysis of these trade receivables is as follows:

The Group holds bank guarantees, other guarantees and credit insurance in respect of some of the past due debtor balances.

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 are as follows:

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 internationally
dispersed customers.