Calderbank offers: A matter of time

Can a Calderbank (Calderbank v Calderbank [1975] 3 All ER 333) offer to settle (without an express time limit) be accepted once the relevant substantive hearing has commenced, or does such an offer lapse at the commencement of the hearing? That was the question at the heart of the appeal in MEF v St George’s Healthcare NHS Trust [2020] EWHC 1300 (QB), [2020] Costs LR 583. The court considered the application of the relevant Civil Procedure Rules on costs and the common law principles of offer and acceptance.