Police in Calais have discovered what French news media are calling un véritable arsenal de guerre – a veritable arsenal of war — on board a London-bound bus.

A Eurolines bus left Amsterdam bound for London via Calais on Tuesday when border police searched baggage and found three loaded automatic pistols, three Smith & Wesson revolvers and a semi-automatic Luger, as well as two Italian-made firearms, a Czech-made firearm, a silencer and almost 500 rounds of 9mm ammunition.

Police have not identified the owner of the firearms. The bus was carrying 35 passengers, all of whom, as well as the driver, have been questioned. DNA tests have been carried out on 12 passengers who joined the bus in Utrecht, in the Netherlands, where the baggage was loaded onto the bus.

Police said technical work was underway on evidence gathered including the DNA.

Prosecutors in Bologne-sur-Mer said Thursday that all passengers and the drive had been left free to go. A judicial investigation is ongoing to establish who owns the baggage.

The find echoes the discovery in Marseille on board a bus from Amsterdam on May 30 of a Kalashnikov linked to the shooting dead of four people at the Jewish Museum in Brussels on May 24. The arms were in baggage belonging to Mehdi Nemmouche, a Frenchman of Algerian origin with links to jihadists in Syria, who was on the bus and is now awaiting extradition from France to face charges in Belgium for the shootings.

British police may be particularly worried that the arms found this week were on board a bus bound for London, as a million-strong demonstration in support of Hamas-controlled Gaza is planned for the city on Saturday.