Puente announced his decision at the end of a lengthy congressional session on Tuesday evening in which he had outlined new rail safety measures and had been grilled by the opposition.

He also said: "I am not only stepping down from my position as minister of transport, but... I am also withdrawing my name from the lists for the early legislative elections."

Puente's position immediately came under scrutiny after the 28 October crash.

The main opposition, the conservative People's Party (PP) and the far-right Vox, were both calling for his resignation - as were some of the government's allies.

They argued that the minister should take responsibility for a high-speed rail system that many Spaniards now regard as unsafe and whose credibility even Socialist Prime Minister Pedro Sánchez admitted was "broken".

The opposition also criticised Puente for appearing to blame human error for the crash, claiming the minister was trying to deflect the blame from his own failings.

But, having said he was going to remain in his post just a few days ago, his resignation appears to have taken many by surprise.

The rail accident and Puente's decision have come at a crucial moment in the Spanish political calendar, with early general elections on 29 November.

Many observers see the accident as a massive electoral setback to the Socialist-led government that will make it impossible for Sánchez to defy the polls and win the election.

Puente's predicament presented him and the prime minister with a dilemma - refusing to resign might look insensitive in the wake of the accident and stepping down could look like acknowledging he and the government were at fault.

In the end, Puente opted for the second option, insisting his decision had been driven by "political dignity".

The prime minister praised his colleague who had "faced up to the situation, provided answers and solutions, and then stepped aside".

"Out of dignity. Of his own accord. Out of respect for the victims," Sánchez added.

Many Spaniards will now ask whether Puente's successors will manage to restore faith in the country's railway system.

In one, a control centre operator is speaking to the driver of the Renfe train, which was having some technical difficulties.

After some exchanges, the control operator tells the driver: "Continue your journey and then proceed under [Lateral Signalling Block], at normal speed with normal operation."

The driver replies: "At normal speed?" To which the controller answers: "Yes."

The Lateral Signalling Block is a back-up system used when the automatic signalling or data transmission system fails.

The driver of the stationary Iryo train says in another audio recording that communication with the train-control system has been lost, and it is not moving.

The train "is stationary in front of the entry signal at Urda", the driver tells the control centre operator. After a series of exchanges, the driver is then told to "resume the journey" normally.

The Iryo driver then contacts the control centre again, according to a later recording, saying they cannot start the train. "The train won't allow me to control the [security] system. That's why I am still stopped in front of the entry signal," they say.

The latter recording suggests that the controller had been notified that the Iryo train remained stationary as the Renfe train approached.

Iryo said its carriages were "struck from behind" by the other train.