| 15 Debtors amounts falling due within one year | | | | Group | | | | Company | | | | 2000 £m | | Restated 1999 £m | | 2000 £m | | Restated 1999 £m | | Trade debtors | | 919 | | 839 | | 352 | | 272 | Amounts recoverable on contracts | | 94 | | 78 | | 18 | | 3 | Amounts owed by subsidiary undertakings | | | | | | 645 | | 606 | joint ventures | | 156 | | 165 | | 129 | | 121 | Corporate taxation | | 11 | | 10 | | 7 | | 10 | Other debtors | | 201 | | 93 | | 40 | | 1 | Prepayments and accrued income 1 | | 210 | | 107 | | 143 | | 44 | | | | 1,591 | | 1,292 | | 1,334 | | 1,057 | | 1Certification costs amounting to £28m(1999 £29m) which were previously included in prepayments have been treated as intangible assets (see note 9). |