Disclaimer: this answer relies on the assumption (stated in the question) that the D.O.B. is being requested as part of the statement of truth and not for some other reason.
I'm not aware of any requirement that the statement of truth must contain a date of birth. I have also never included one in a statement of case, nor does Practical Law's standard document for a contractual debt claim defence (paywall) include one in the statement of truth or anywhere else.
The relevant rules, for a litigant in person providing their own defence, come from Practice Direction 16, CPR 22, and Practice Direction 22 of the Civil Procedure Rules.
Requirements for statement of truth
The requirements for a statement of truth are fairly straightforward. A defence must include include one, and the statement of truth must:
- Contain a statement in the prescribed wording.
- Be signed.
- Be dated with the date on which it was signed.
- State the name of the person signing, underneath the signature.
CPR 22.1(1): (1) The following documents must be verified by a statement of truth – (a) a statement of case; [...]
16 PD 10.1: The defence must be verified by a statement of truth in the
form specified in paragraph 2.1 of Practice Direction 22.
CPR 22.1(4): Subject to paragraph (5), a statement of truth is a
statement that – (a) the party putting forward the document; (b) [...]
; or (c) [...], believes the facts stated in the document are true.
CPR 22.1(6): The statement of truth must be signed by - (a) in the case
of a statement of case, a response or an application – (i) the party
or litigation friend; [...]
22 PD 2.1: The form of the statement of truth verifying a statement of
case, a response, an application notice, a certificate of reasons or a
notice of objections should be as follows:
‘[I believe][the (claimant or as may be) believes] that the facts
stated in this [name document being verified] are true. I understand]
[The (claimant or as may be) understands that proceedings for contempt
of court may be brought against anyone who makes, or causes to be
made, a false statement in a document verified by a statement of truth
without an honest belief in its truth.’
22 PD 2.5: A statement of truth must be dated with the date on which it
22 PD 3.9: The individual who signs a statement of truth must print his
full name clearly beneath his signature.
Consequences of failure to comply with requirements
The consequences of failing to include a valid statement of truth are as follows:
- You cannot rely on the contents of the defence as evidence until it is verified by a compliant statement of truth.
- The claimant can apply for you to be given an opportunity to provide a statement of truth by a specified deadline, failing which the defence will be struck out.
- The claimant will usually be awarded costs for such an application.
CPR 22.2(1): If a party fails to verify his statement of case by a
statement of truth – (a) the statement of case shall remain effective
unless struck out; but (b) the party may not rely on the statement of
case as evidence of any of the matters set out in it.
CPR 22.2(2): The court may strike out a statement of case which is not
verified by a statement of truth.
CPR 22.2(3): Any party may apply for an order under paragraph (2).
22 PD 4.1: If a statement of case is not verified by a statement of
truth, the statement of case will remain effective unless it is struck
out5, but a party may not rely on the contents of a statement of case
as evidence until it has been verified by a statement of truth.
22 PD 4.2: Any party may apply to the court for an order that unless
within such period as the court may specify the statement of case is
verified by the service of a statement of truth, the statement of case
will be struck out.
22 PD 4.3: The usual order for the costs of an application referred to
in paragraph 4.2 will be that the costs be paid by the party who had
failed to verify in any event and forthwith.