“(1) The court has discretion as to— (a) whether costs are payable by one party to another; (b) the amount of those costs; and (c) when they are to be paid. (2) If the court decides to make an order about costs— (a) the general rule is that the unsuccessful party will be ordered to pay the costs of the successful party; but (b) the court may make a different order. … (4) In deciding what order (if any) to make about costs, the court will have regard to all the circumstances, including— (a) the conduct of all the parties; (b) whether a party has succeeded on part of its case, even if that party has not been wholly successful; and (c) any admissible offer to settle made by a party which is drawn to the court’s attention, and which is not an offer to which costs consequences under Part 36 apply”