The international hunt for Ashya King, the missing five-year-old boy with a brain tumour, came to a dramatic end on Saturday night when his parents were arrested in Spain and their son was taken from them and sent to a local hospital for urgent medical treatment.

Brett and Naghemeh King, 45, were spotted in their Hyundai people carrier around 10pm by police in Velez Malaga, a town an hour to the east of Marbella. The couple, who were being held under an international arrest warrant on suspicion of neglect, had checked into a hostel about 14 miles away in Benajaraf on the Costa del Sol where they had left their six other children.

Ashya had been removed from Southampton general hospital by his parents against medical advice last week. He was last seen with the rest of his family on a ferry travelling from Portsmouth to Cherbourg on Thursday afternoon. At a press conference on Saturday night, the assistant chief constable of Hampshire, Chris Shead, said: "Just before 9pm UK time [Spanish police] found Ashya. They stopped the vehicle that we've been circulating the details of and in the vehicle was Ashya's parents and Ashya. We don't have many details as to Ashya's condition in this time but we do know he was showing no visible signs of distress."

Shead added that the parents had been arrested and taken to a police station. "There are no winners in this situation," he said. "This must be a very distressing time for Ashya's family. Thankfully we have found Ashya. Our number one aim has been to ensure he gets the welfare he needs. We've immediately contacted Southampton General Hospital to make sure they have the details of Ashya's medical team in Spain. Tomorrow morning we will be sending a team of police to Malaga and they will continue the investigation."

In a YouTube video posted by Ashya's eldest brother, Naveed, earlier in the night, Brett King spoke for 10 minutes explaining the couple's decision to take their son out of hospital and seek medical help abroad. He complained about the "trial and error" treatment Ashya had been receiving on the NHS and called for the hunt to be called off, saying the family had become "refugees almost" and asked that they be left in peace. Sitting on a bed with his son lying limply in his lap in a nappy and T-shirt, King, 51, said: "We've been labelled as kidnappers, putting [Ashya's] life at risk, neglect."

He then pointed to food supplements at the side of the bed, connected to Ashya by tubes. "There's been a lot of talk about this machine, as you see it's all plugged in. We've got loads of these feeds, we've got iron supplements and Calpol," he said. "As you can see there's nothing wrong with him, he's very happy actually, since we took him out of hospital he's been smiling a lot more."

Online comments to the video were overwhelmingly supportive of the Kings, with people asking police to treat them with "compassion and understanding".

King said in the video that Ashya's health deteriorated after initial successful treatment to remove his tumour and they argued with doctors over next steps. The Kings wanted a specific type of cancer treatment called proton beam treatment that is not available on the NHS. Brett King said: "We asked the NHS if we could please go to America, to Switzerland, or another country to get proton beam, because it's so much better for children with brain cancer. It zones in on the area, whereby normal radiation passes right through his head and comes out the other side and destroys everything in his head. They looked at me straight in the face and said with his cancer – which is called medulloblastoma – it would have no benefit whatsoever."

King said the hospital threatened to take out an emergency protection order that would have banned them from coming on to the ward. "After that I realised I can't speak to the oncologist at all, because if I actually ask anything or give any doubt I wasn't in full accord with them, they were going to get a protection order which meant in his deepest, darkest hour [we] wouldn't be there to look after him. That's such a cruel system.

"We decided to try and sort it out ourselves but now we're refugees almost. We can't do anything. The police are after us. The things we want to do to raise the money to pay for the proton beam, they've prevented it now. So my son is being treated and he's doing fine. We're very happy with his progress. We're not neglecting him. He has everything he had in hospital. Speak to the nurses, have they seen him move as much as this? I'm not coming back to England if I cannot give him the treatment I want."

On Saturday afternoon, Hampshire police said they had "positive information" that the Kings' car had been seen in Spain, where they own a villa in Marbella. Spanish police visited the villa but there had been no sign of the family, fuelling fears about Ashya's condition.

His last operation had been seven days ago. Police had warned that his battery-operated feeding system was likely to have expired and feared that his health would deteriorate rapidly unless he received medical care.

Appeals for help in finding Ashya had been made in Italian, French and Spanish. Interpol sent out a missing persons alert to each of its 190 member countries.

A family friend said earlier that Ashya's family had run away in desperation: "This is my mother's friend, she has run away in desperation because they cannot accept that there is nothing that can be done for their son and want to look for help abroad," Katie Fletcher wrote on Hampshire police's Facebook page.

"Please don't judge. They are a very sweet, loving family and I can only believe they are doing this because they want to help their son."

Naveed first posted a YouTube video on 23 July speaking about his sibling's illness. "Everyone is sending their love now," he said. "We love you so much and we want to see you very soon and I love you so much and can't wait to see you."

The Office of Public Information for Jehovah's Witnesses, who refuse blood transfusions on religious grounds, confirmed that Ashya's parents were followers of the religious movement.

A spokesman said there was "absolutely no indication" that the family's decision to remove their son from hospital was "motivated by any religious convictions".

Brett King's mother, Patricia, said her son was "the most caring and wonderful father you could ever have".

Legal experts said it was unlikely that the Kings had committed an offence by taking Ashya out of hospital. Professor Penney Lewis, of King's College London, said: "There has never been a case where parents have done something like this and they have been prosecuted."

Shead said the six-and-a-half-hour gap between Ashya being taken from hospital and police being called would be considered "further down the line".

University Hospital Southampton NHS Foundation Trust, which is in charge of Southampton general hospital, said Ashya was allowed to leave the ward under his parents' supervision and hospital staff raised the alarm when the length of his absence became a cause of concern.