18. Contract assets, trade and other receivables

Contract assets of £48,840,000 (2022: £74,898,000) mainly reflect the Group's right to consideration for work completed but not yet invoiced at the year end. These are transferred to trade receivables when there is an unconditional right to payment. The reduction in contract assets is driven by the stage of completion of construction contracts. At 26 March 2022, there were several significant contracts in the early stages of completion and therefore not yet eligible to be billed.

The average credit period taken on revenue, calculated on a count-back basis to make appropriate allowance for monthly revenue phasing, is 85 days (2022: 69 days). No interest is charged on receivables.

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

Before accepting any new customer, the Group uses an external credit rating agency to assess the potential customer's credit quality and defines credit limits by customer. It is Group policy that adequate credit insurance is taken out on all customers to manage the exposure that may arise as the contractual work proceeds. The Group's executive risk committee reviews situations where adequate credit insurance on the Group's customers cannot be purchased in the present economic climate as required. The Group has rigorous procedures in place for monitoring and obtaining settlement of retentions in a prompt manner. Overdue retentions at 25 March 2023 were £nil (2022: £nil).