The 22,400–gt Sirena Seaways (built 2002) made heavy contact at Harwich on 22 June last year, causing "considerable damage" to the fore-end of the vessel.

The linkspan at the port collapsed into the water and supporting structures were severely damaged.

The UK Marine Accident Investigation Branch (MAIB) said propulsion control records showed the starboard system remained set at about 63% ahead throughout the incident.

No defects were found and it was "considered most likely" that the button to activate the back-up control system for the starboard propulsion system was "inadvertently pressed" during the early stages of the entry into the port, MAIB found.

This bypassed normal control and was not noticed by the crew.

The systems was still operating at 63% ahead for two hours after the collision, hampering attempts to pull the vessel from the damaged berth.

Recommendations have been made to DFDS to review the need for regular bridge and crew resource management training.