The courts (and arbitrators) have the power to decide whether a party is entitled to interest on its claim.
An adjudicator does not have this power. In adjudication, a party does not have the right to claim interest unless the contract expressly allows it to do so, or unless there is a specific statutory right.
For example, the JCT forms of contract provide for interest where payment of a certified sum is late. However, there is no express right to interest in the JCT forms where a tribunal decides that a contractor is entitled to loss and expense.
A judge can award interest relating to a loss and expense claim using his or her discretion under section 35A Senior Courts Act 1981. Arbitrators can also award interest at their own discretion pursuant to section 49 of the Arbitration Act 1996. There is no equivalent statutory provision in relation to adjudication.
The recent consultation regarding the proposed changes to the Scheme for Construction Contracts asked the construction industry whether adjudicators should have the discretion to award interest in adjudications brought under the scheme. This would seem fair. We will have to wait to see whether it is implemented.