A train driver suspected of causing Spain's deadliest rail disaster for 70 years has been arrested.

Investigators are looking into possible failings by the driver, named locally as Francisco Jose Garzon Amo, after the Madrid- to-Ferrol service derailed on Wednesday night.

Police confirmed the number of dead as 78, down from the 80 reported earlier.

A spokesman for Spain's National Police said Mr Garzon Amo, 52, was arrested in hospital on suspicion of causing the accident but would not say if officers had already questioned him.

Some 72 of those killed in the catastrophe have now been formally identified, while DNA results for the remaining six are expected in the coming days.

The revised death toll came as forensic scientists matched body parts with each other at a makeshift morgue in a sports arena.

One Briton has been confirmed by the Foreign Office to be among the 168 injured passengers, while 32 people are still believed to be in a critical condition.

Early indications suggested the train was travelling at about 118mph – more than twice the 50mph speed limit – when it crashed while heading into a curve as it approached the city of Santiago de Compostela.

A investigation is also looking into whether the Alvia 730 series train's in-built speed regulation systems failed.

Nationals from the US, Mexico and Algeria are believed to be among the dead. One US woman killed in the wreck has been named as Ana Maria Cordoba, an employee of a diocese near Washington DC.

According to reports in the Spanish media, after realising the magnitude of the disaster Garzon Amo said: "I f***** up, I want to die."

In March 2012, the 30-year employee of Spanish train operator Renfe allegedly posted boasts on Facebook about how fast he was driving a train and joked about racing past police.

He is believed to have taken control of the train from another driver about 65 miles south of Santiago de Compostela.

Spanish prime minister Mariano Rajoy, who was born in the city, visited the crash scene on Thursday and declared three days of national mourning.

The full horror of the disaster was revealed in harrowing video footage of the moment the train derailed.

Posted on YouTube, the security camera footage shows the middle carriages smashing into a wall before the engine crashes on to its side.

The derailment left a "Dante-esque" scene of devastation, with toppled and smashed carriages lying alongside the track as bodies were laid beside the line and bloodied survivors were carried to safety.

The crash is the worst Spain has experienced since a three-train accident in a tunnel in the northern Leon province in 1944.

Due to heavy censorship at the time, the exact death toll for the Torre del Bierzo disaster has never been established.

The official figure was given as 78 dead, but it is thought as many as 250 could have been killed.

There was another serious accident in Spain in 1972 when a Madrid-to-Cadiz express collided head-on with a local train on the outskirts of Seville. Some 77 people died, with more than 100 injured.

The latest incident comes less than two weeks after six people were killed and scores injured in a train crash just south of Paris.