Court appointed experts (ctu) are very common in Italy and their function is to assist the court on any technical issues requiring specialist knowledge. Each party has the right to appoint their own expert (ctp) to dialogue with the court appointed one and make sure their views are taken into account when the ctu draws up the report for the court. the best translation in your case is defendant's expert as opposed to the plaintiff's expert and the court appointed expert.

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Note added at 2002-07-26 14:39:27 (GMT) Post-grading
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with reference to the term that was entered in the glossary remember that ctp means the expert appointed by a party and therefore ctp could be translated in numerous ways depending on which party appointed it: defendant\'s expert, plaintiff\'s expert, claimant\'s expert, applicant\'s expert, respondent\'s expert etc. etc.