But in the prosecution of Wyclif they resolved to return blow for blow.

In February 1377 he was summoned before Bishop Courtenay of London to answer for his heretical propositions concerning the wealth of the Church.
The Duke of Lancaster accepted the challenge as really given to himself, and stood by Wyclif's side in the Consistory Court at St.Paul's.

But no trial took place.

Fierce words passed between the nobles and the prelate: the Duke himself was said to have threatened to drag Courtenay out of the church by the hair of his head; at last the London populace, to whom John of Gaunt was hateful, burst in to their Bishop's rescue, and Wyclif's life was saved with difficulty by the aid of the soldiery.

But his boldness only grew with the danger.