In respect of costs payable by order and included in a bill of costs for detailed assessment, the receiving party may be entitled to interest under Section 17 of the Judgments Act 1838 or, in County Court cases, under Section 74 of the County Courts Act 1984. If so the entitlement to interest begins on the date upon which the order for costs was made (not the date upon which the costs were assessed). However,
(i) Under CPR 40.8 and CPR 44.2(6)g the court has power to order interest on costs to run from a date other than the date of judgment; and
(ii) In Involnert Management Inc v Apilgrange Limited and Others  EWHC 2834 (Comm) it was held that the date from which Judgments Act interest runs should be postponed, in that it should run from the date prescribed by the rules for commencing detailed assessment proceedings, namely three months from the date upon which the costs order was made.
In respect of the costs of the detailed assessment proceedings, the interest begins to run from the date of the default, interim or final costs certificate, as the case may be. For certificates issued from 1 April 2013, the court may order otherwise under CPR 47.20(6).
In respect of costs payable by contract (e.g. costs payable to a solicitor by a client or former client) the entitlement to interest normally depends upon the terms of that contract. Also, a statutory right to interest may arise under the Solicitors (Non Contentious Business) Remuneration Order 2009 or the Late Payment of Commercial Debts (Interest) Act 1998.