Keith Schembri will not participate in any police interrogation until he learns the outcome of a magisterial inquiry into an alleged kickback from passport sales, his lawyer has said. 

The former prime minister's chief aide is being held at police headquarters in Floriana after his arrest at 12.30am on Tuesday, hours after news broke that his assets have been frozen on suspicion of money laundering.

In a statement outside police headquarters, his lawyer Edward Gatt said the conclusions of the magisterial inquiry should be made public.

"We are insisting with the police that they disclose what the conclusions of the magistrate were. Before these conclusions are made public, we are not going to participate in the interrogation process," Gatt said.

On Tuesday morning Schembri's lawyers filed an urgent request in court for police to disclose the evidence they have against their client.

Lawyers Gatt and Mark Vassallo said Schembri was informed by police that the arrest was in connection with the conclusion of the inquiry into the alleged kickbacks.

Gatt said Schembri had testified in the inquiry but what was important now were the conclusions reached by the magistrate.

The inquiry dates back to 2017 when allegations emerged that Schembri received €100,000 in kickbacks from Nexia BT's Brian Tonna over passport sales. Tonna and Karl Cini, both Nexia BT partners, have also been arrested. 

The outcome of that inquiry concluded within recent weeks, and handed to the police, who said they were studying it for "possible actions".

Then late on Monday night, it emerged that a court had issued an order to freeze all the assets held by Schembri, on suspicion of money laundering.

Nexia BT is among the long list of companies and people subject to a freezing order placed on moveable and immovable property.