The court has a discretionary power to grant an injunction to restrain the breach of a negative term of a contract even though the positive part of the contract is not specifically enforceable, e.g. in the case of a contract of personal service. The rationale of the jurisdiction to grant an injunction to restrain a breach of contract was explained by Lord St Leonards LC, in Lumley v Wagner (1852) 1 De GM & G 604:

Wherever this court has not proper jurisdiction to enforce specific performance, it operates to bind men's consciences, so far as they can be bound, to a true and literal performance of their agreements; and it will not suffer them to depart from their contracts at their pleasure, leaving the party with whom they have contracted to the mere chance of any damages which a jury may give. The exercise of this jurisdiction has, I believe, had a wholesome tendency towards the maintenance of that good faith which exists in this country to a much greater degree perhaps than in any other; and although the jurisdiction is not to be extended, yet a judge would desert his duty who did not act up to what his predecessors have handed down as the rule for his guidance in the administration of such an equity.