UBS AG (UBSN)’s top employment lawyer in Europe denied claims by former trader Kweku Adoboli that bank workers are barred from testifying in his defense at a trial over a $2.3 billion trading loss.

While UBS contracts may prevent current or former employees from disparaging the Zurich-based bank or sharing intellectual property, there’s nothing stopping them from answering questions in litigation, Jamie Howard, the bank’s head of employment law for Europe, the Middle East and Africa, said yesterday in London.

Regardless of the “implied duty of fidelity” in such contracts, employees may testify against the bank “if required by law,” Howard said.

Adoboli, originally from Ghana, is on trial for fraud and false accounting over the loss caused from unauthorized trades. Prosecutors asked Howard to testify after Adoboli’s lawyer suggested workers were being prevented or discouraged from helping bolster the former trader’s defense.

Adoboli ended eight days of testimony by saying text messages between him and his girlfriend in the days before his arrest on Sept. 14, 2011, support his claim that he didn’t act alone. He denied allegations by prosecutors that the texts may have been staged in anticipation of a future defense.

Adoboli is accused of hiding the risk of his trades by booking fake hedges at the Swiss bank and then hiding profit to cover future losses before market fluctuations made his positions untenable. As part of his defense, he claimed three others on the exchange-traded-funds desk knew of or took part in the activities and chose to let him take the fall alone.

None of the other traders have been charged.