| 2018
£m | 2017
£m |
| Amounts falling due within one year: | | |
| Amounts receivable for the supply of services | 120.1 | 114.2 |
| Other receivables | 17.2 | 16.8 |
| Prepayments | 9.0 | 9.4 |
| 146.3 | 140.4 |
| Amounts falling due after more than one year: | | |
| Other receivables and prepayments | 1.4 | 1.0 |
The average credit period given to customers for the supply of services as at 31 December 2018 is 64 days (2017: 63 days). An allowance has been made for estimated irrecoverable amounts from the supply of services of £5.1m (2017: £5.5m). This allowance has been determined by reference to expected credit losses.
The carrying amount of trade and other receivables approximates their fair value.
Included in the Group's trade receivables balance are debtors with a carrying amount of £32.0m (2017: £29.2m) 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 15 days to 68 days.
Ageing of past due but not impaired receivables:
| 2018
£m | 2017
£m |
| 31–60 days | 15.1 | 13.9 |
| 61–90 days | 11.1 | 11.1 |
| 91–120 days | 4.1 | 2.1 |
| Greater than 120 days | 1.7 | 2.1 |
| 32.0 | 29.2 |
Movement in the allowance for doubtful debts:
| 2018
£m | 2017
£m |
| At 1 January | 5.5 | 7.1 |
| Impairment losses recognised | 1.6 | 1.8 |
| Amounts written off as uncollectable | (0.3) | (2.4) |
| Impairment losses reversed | (1.8) | (1.0) |
| Exchange differences | 0.1 | – |
| At 31 December | 5.1 | 5.5 |
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 £6.2m (2017: £6.6m). 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:
| 2018
£m | 2017
£m |
| Less than 3 months | 0.1 | 1.5 |
| 3-12 months | 3.8 | 3.7 |
| Over 12 months | 2.3 | 1.4 |
| 6.2 | 6.6 |