This question was considered by Coulson J in Milton Keynes v Viridor  EWHC 2764 (TCC).
The Defendant sought a court order requiring a new party to be added as a second defendant, against the Claimant's wishes. The judge considered that the proposed joinder did not fall within CPR 19.2(2). This permits the court to order joinder where it is "desirable" so that the court can resolve all the matters in dispute, or where there is an issue between the new party and an existing party connected to the matters in dispute, and it is desirable to add the new party so the court can resolve the issue.
the judge held that the proposed joinder did not fall within either of these: there was no matter in dispute between the Claimant and the new party, nor was there any pleaded issue between the Defendant and the new party.
Whilst this may have been sufficient to determine the application, the judge went a step further.
Noting there was no authority on the issue, the judge held that the Court has no power to join a party as a defendant, against the Claimant's wishes. A claimant was entitled to sue whomever he wishes and cannot be forced into proceedings against another party, potentially incurring an adverse costs liability.