Trade and other receivables

	2017 £m	2016 £m
Amounts falling due within one year:
Amounts receivable for the supply of services	114.2	106.4
Other debtors and prepayments*	26.2	19.9
	140.4	126.3
Amounts falling due after more than one year:
Other debtors and prepayments*	1.0	0.4

* Other financial assets include prepayments of £9.4m (2016: £8.0), which are not included as financial assets under IFRS 7.

The average credit period given to customers for the supply of services as at 31 December 2017 is 63 days (2016: 63 days). An allowance has been made for estimated irrecoverable amounts from the supply of services of £5.5m (2016: £7.2m). This allowance has been determined by reference to past default experience.

The directors consider that the carrying amount of trade and other receivables approximates their fair value.

Credit risk

The Group's principal financial assets are bank balances, cash and trade and other receivables.

The Group's credit risk is primarily attributable to its trade receivables. The amounts presented in the balance sheet are net of allowances for doubtful receivables. An allowance for impairment is made where there is an identified loss event which, based on previous experience, is evidence of a reduction in the recoverability of cash flows.

The credit risk on liquid funds and derivative financial instruments is limited because the counterparties are banks with high credit-ratings assigned by international credit-rating agencies.

The Group has no significant concentration of credit risk, with exposure spread over a large number of counterparties and customers. Further disclosure of the Group's financial instrument risk management activities is set out in note 18.

Included in the Group's trade receivable balance are debtors with a carrying amount of £29.2m (2016: £21.9m) which are past due at the reporting date for which the Group has not provided as there has not been a significant change in credit quality and the amounts are still considered recoverable. The Group does not hold any collateral over these balances.

The average credit terms offered to customers is 36 days, with a range from 14 days to 67 days.

Ageing of past due but not impaired receivables:

	2017 £m	2016 £m
31–60 days	13.9	12.6
61–90 days	11.1	5.6
91–120 days	2.1	1.2
Greater than 120 days	2.1	2.5
	29.2	21.9

Movement in the allowance for doubtful debts:

	2017 £m	2016 £m
At 1 January	7.1	5.9
Impairment losses recognised	1.8	1.9
Allowance acquired with businesses	–	0.1
Amounts written off as uncollectable	(2.4)	(0.9)
Impairment losses reversed	(1.0)	(0.7)
Exchange differences	–	0.8
At 31 December	5.5	7.1

In determining the recoverability of a trade receivable the Group considers any change in the quality of the trade receivable from the date credit was initially granted up to the reporting date. The concentration of credit risk is limited due to the customer base being large and unrelated. Accordingly the directors believe that there is no further credit provision required in excess of the allowance for doubtful debts.

Included in the allowance for doubtful debts are individually impaired trade receivables with a gross balance of £6.6m (2016: £10.2m). The impairment recognised represents the difference between the carrying amount of these trade receivables and the present value of the expected proceeds. The Group does not hold any collateral over these balances.

Ageing of impaired trade receivables:

	2017 £m	2016 £m
Less than 3 months	1.5	1.6
3–12 months	3.7	2.9
Over 12 months	1.4	5.7
	6.6	10.2

Cash and bank balances

Cash and bank balances comprise cash held by the Group and short-term bank deposits with an original maturity of three months or less. The carrying amount of these assets approximates to their fair value. A breakdown of significant cash and bank balances by currency is as follows:

	2017 £m	2016 £m
Sterling	24.5	3.3
Euro	6.0	2.2
US Dollar	5.8	3.7
Swedish Krona	1.5	1.0
Other	3.2	1.8
Total cash and bank balances	41.0	12.0