“(a) the terms of any Part 36 offer; (b) the stage in the proceedings when any Part 36 offer was made, including in particular how long before the trial started the offer was made; (c) the information available to the parties at the time when the Part 36 offer was made; and (d) the conduct of the parties with regard to the giving or refusing to give information for the purposes of enabling the offer to be made or evaluated.”