Contractor Claim for Increased Costs under Loss and Expense

Can a contractor claim for increased costs under a JCT Design & Build as part of his loss and expense if there is no fluctuation clause?

Yes, if the relevant delay caused material to be purchased later than it otherwise would have been and at a higher price. However, the Contractor is obliged to mitigate the loss and should have purchased the material when originally required, if reasonably possible, to avoid the cost increase