Legislative provisions on refunds are to be found in the relevant collection and enforcement regulations for central and local lists. Unsurprisingly, the legislation contains specific provision governing the situation where there has been, for whatever reason, an overpayment of rates. Regulations make provision for the addition of interest to repayments or credits made under the collection and enforcement regulations. If the billing authority fails in its obligation to refund the overpayment, the ratepayer may take proceedings in a 'court of competent jurisdiction' to recover it. Where the regulations do not provide a right to recover an overpayment, the common law may do so. The common law recognises a general right to restitution of money paid pursuant to an unlawful levy of tax. This extends to payments of rates. Estoppel operates to prevent a person from going back on a previous assertion. It requires a clear assertion which leads the other party to change his position to his detriment.