Part 16 of the CPR states what should be included in a defence:
Denials are use for any facts that would have been within your knowledge or where you have an alternative version of events. Any denial must be backed up by reasons in your defence and any alternative version of events should be stated in the defence. Facts which are admitted are not an issue and evidence of them is not required. There may be allegations that the you cannot admit or deny, in which case the claimant will be required to prove the allegation.
The amount of money claimed is deemed to be disputed. If the value of the claim is disputed, the defendant must say why and give an estimated value.
A defence must set out any matter which raises issues not included in the particulars of claim, for example, the issues of limitation (when a debt is statute barred under the Limitation Act) or fraud.
In the case of limitation, statute barred is an absolute defence, and all that’s required is to state that fact in your defence.
In some cases, it may be necessary to amend your defence. This is covered by CPR 17.1.Once your defence has been served on the claimant, you’d need consent from the claimant to amend your defence. You will need to fill in an N244 form application notice with a copy of your defence and a statement of truth. See applications.
If the Claimant refuses to allow you to amend your defence, you will have to make an application to the Court to amend the Defence under CPR 17.1(2)(b) as noted above.