Witness in civil case?

If the claimant in a civil matter had made various claims, which he is quite
unable to support with any credible evidence whatsoever, would it be
possible for defendants to require witnesses to attend regarding such
claims, and if they refused to do so, then subpoena them to attend?

This relates specifically to claims of impotence, that apparently has
resulted from name calling on here, and as the claimants teenage girlfriend
obviously has direct knowledge of his problems in this area, it would seem a
matter of some importance that she give evidence in regard to the claimants
supposed problems (for which he is claiming £100K!).



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