16 Debtors amounts falling due after one year | | | Group | | | | Company | | | 2000 £m | | Restated 1999 £m | | 2000 £m | | Restated 1999 £m | | Trade debtors | 18 | | 45 | | 17 | | 40 | Amounts recoverable on contracts | 97 | | 39 | | 93 | | 39 | Amounts owed by subsidiary undertakings | | | | | 13 | | 25 | joint ventures | 57 | | 45 | | 43 | | 44 | Corporate taxation | 26 | | 19 | | 26 | | 19 | Other debtors | 49 | | 66 | | | | | Prepayments and accrued income 1 | 78 | | 36 | | 76 | | 36 | Prepaid pension contributions | 157 | | 105 | | 5 | | 5 | | | 482 | | 355 | | 273 | | 208 | | 1Certification costs amounting to £13m(1999 £16m) which were previously included in prepayments have been treated as intangible assets (see note 9). |