"(a) The lateness by which an amendment is produced is a relative concept ... An amendment is late if it could have been advanced earlier, or involves the duplication of cost and effort, or if it requires the resisting party to revisit any of the significant steps in the litigation (such as disclosure or the provision of witness statements and expert's reports) which have been completed by the time of the amendment... (c) The history of the amendment, together with an explanation for its lateness, is a matter for the amending party and is an important factor in the necessary balancing exercise ... In essence, there must be a good reason for the delay ... (d) The particularity and/or clarity of the proposed amendment then has to be considered, because different considerations may well apply to amendments which are not tightly-drawn or focused. (e) The prejudice to the resisting parties if the amendments are allowed will incorporate, at one end of the spectrum, the simple fact of being ‘mucked around’, to the disruption of and additional pressure on their lawyers in the run-up to trial, and the duplication of cost and effort at the other. If allowing the amendments would necessitate the adjournment of the trial, that may be an overwhelming reason to refuse the amendments. (f) Prejudice to the amending party if the amendments are not allowed will, obviously, include its inability to advance its amended case, but that is just one factor to be considered ... Moreover, if that prejudice has come about by the amending party's own conduct, then it is a much less important element of the balancing exercise ..."