17:47 02 September 2014
Brett and Naghemeh King are being held by police in Madrid after they took their son, who was suffering from a brain tumour, from the hospital without permission before travelling to Spain.
There has been growing calls for their release after they spent another night away from their ailing son.
Deputy Prime Minister Nick Clegg said that his “heart goes out” to the parents.
"A little boy is on his own in a hospital, I would like to see him with his family as soon as possible," he said.
"As far as I can make out, this is a family in a state of real anguish who have taken this exceptional step of moving their sick child to another country because they think that's what is best for their child."
Meanwhile, the Crown Prosecution Service (CPS) said that the couple is under immediate review after further evidence was provided.
A spokesman said: "Once this evidence has been thoroughly examined, a decision will then be made as to whether a prosecution is required."
Meanwhile, the couple's lawyer in Spain, Juan Isidro Fernandez Diaz, said they are preparing to take legal action against Southampton General Hospital.
He said they "wanted the very best for their child."
"They never thought that they committed any crime in the UK," he added.