Is acting for a vendor and purchaser in a conveyancing transaction prohibited?

No, see the answer to the above. By operation of Rule 11, the solicitor could consider obtaining the informed consent of both clients before acting for both parties. However, even with the informed consent, a solicitor must exercise independent judgement to determine whether a conflict is likely to arise even where one does not currently exist. Consideration needs to be given to any divergence in the parties’ positions which has arisen or may arise, e.g. has there been a falling out or is it in the interests of one party to delay settlement?