As per the Civil Procedure Rules, they can only raise allegations that were in the defence.
That is because the defence is a document which sets the foundation of a case for this very reason.
The Civil Procedure Rules states:
(1) In his defence, the defendant must state –
(a) which of the allegations in the particulars of claim he denies;
(b) which allegations he is unable to admit or deny, but which he requires the claimant to prove; and
(c) which allegations he admits.
(2) Where the defendant denies an allegation –
(a) he must state his reasons for doing so; and
(b) if he intends to put forward a different version of events from that given by the claimant, he must state his own version.
(3) A defendant who –
(a) fails to deal with an allegation; but
(b) has set out in his defence the nature of his case in relation to the issue to which that allegation is relevant,
shall be taken to require that allegation to be proved.
(4) Where the claim includes a money claim, a defendant shall be taken to require that any allegation relating to the amount of money claimed be proved unless he expressly admits the allegation.
(5) Subject to paragraphs (3) and (4), a defendant who fails to deal with an allegation shall be taken to admit that allegation.
(6) If the defendant disputes the claimant’s statement of value under rule 16.3 he must –
(a) state why he disputes it; and
(b) if he is able, give his own statement of the value of the claim.
(7) If the defendant is defending in a representative capacity, he must state what that capacity is.
(8) If the defendant has not filed an acknowledgment of service under Part 10, the defendant must give an address for service.
Therefore if it was not pleaded in the defence it can not be rasied. So whilst it may be in evidence in the form of a witness statement a Judge should ignore it.
They would need to apply for permission to amend their defence so these new documents are included. If they do not, then they can not raise it.
Can I clarify anything for you about this today, please?
If you need anything further I am available for a follow up at no extra cost.