The Court of Appeal laid down guidelines in Ridehalgh v Horsefield [1994] Ch 205, CA to assist the court in deciding whether a legal representative has acted improperly, unreasonably or negligently:

(i) acting “improperly” includes conduct which would ordinarily be held to justify disbarment of barristers, striking off from the roll of solicitors, suspension from practice or other serious professional penalty;

(ii) acting “unreasonably” describes conduct which is vexatious, or designed to harass the other side rather than advance the resolution of the case;

(iii) acting “negligently” denotes, in an untechnical way, failure to act with the competence reasonably expected of ordinary members of the legal profession.

In general, wasted costs applications should be left until after the end of the trial. It is usual for the aggrieved party rather than the Court to raise the issue of wasted costs, but the Court can make a wasted costs order against a legal representative of its own initiative.