Sahil Saeed and his father Raja Naqqash Saeed are believed to be on a plane back to Manchester from Islamabad.
The five-year-old was released on Tuesday after being snatched at gunpoint in Pakistan two weeks ago.
He was reunited with members of his family, including his father, at the home of the British High Commissioner today.
Footage released of the reunion showed Sahil sending a message to his mother back home.
Prompted by his father, the five-year-old said: "Mummy, I miss you. Mummy, I love you."
A spokesman for the commission said: "Everyone was in very good spirits and of course delighted about his return.
"Sahil was playing football with his father in the garden and seemed really happy."
A statement released by Mr Saeed said he was "completely overjoyed" at being reunited with his son.
The statement continued: "Sahil is doing well, is in good spirits, and can't wait to return to the UK to see his mum, his family, and join his friends back at school.
"I would like to pay tribute to the tireless efforts of the Pakistani and UK authorities that resulted in the safe return of Sahil to us. I would also like to thank everyone for their messages of support that my family and I have received over the course of the last two weeks.
"As we return back to the UK, I ask that the media shows restraint and respects our family's privacy as we spend some quality time with Sahil."
The pair were on holiday with other relatives in Jhelum in the Punjab region when Sahil was snatched by gunmen on March 4.
He was found by locals wandering alone in a field around 15 miles away on Tuesday and handed over to police.
The boy was looked after by British officials while his father travelled from the family home in Oldham, Greater Manchester.
Last night details emerged about the abduction and the police investigation, which involved Pakistani, UK, French and Spanish officers.
Spanish police said Sahil's father went to Paris to pay a £110,000 ransom for his release.
Surveillance officers watched him make the transfer, saw the recipients divide up the cash, and later swooped on a number of suspects, according to a police statement.
After the youngster was freed, three people - two Pakistani men and a Romanian woman - were arrested when police raided a flat in Constanti, around 60 miles from Barcelona. About £105,000 in cash was also recovered.
Two of the suspects were followed from Paris, and all three are due to appear in court in Spain today.
Two other people, accused of helping the kidnappers, were also arrested in the French capital.
A £100,000 ransom demand for Sahil's safe return emerged shortly after the boy was taken.
Interpol alerted Spanish authorities to the abduction and discovered the first call demanding a ransom was made from Spain. A series of other calls were made from the country.
Mr Saeed, 28, returned to Manchester four days after the abduction as instructed by the kidnappers, but was then told to go to Paris with the money.
Police were watching when the cash was handed over on a street in the French capital and began monitoring the suspects as they waited for news of the child's release, Spanish police said.
Mr Saeed's return to the UK was reportedly against the wishes of Pakistani police, who wanted him to stay in the country as a witness.
After he came back, Greater Manchester Police said he was working with them to try to recover Sahil.
The boy's extended family reportedly rallied round to raise the ransom demand, selling jewellery and heirlooms.
Sahil's mother, Akila Naqqash, 31, spoke this week of her joy after hearing that her boy was safe.
Speaking from the family home in Oldham, she said: "I need to see him with my own eyes to believe it. The police are looking after him. We are just watching the news. We are not travelling out there.
"He will fly back but we don't know when yet."
Mrs Naqqash, who also has two daughters aged four and 21 months, said she would give him "a big kiss and cuddles" on his return.
Prime Minister Gordon Brown, on a visit to a new cancer treatment unit in Sahil's home town Oldham, welcomed the boy's return to the UK.
Mr Brown said: "I do think it is very good news. After 12 days, Sahil will be able to return to this country.
"I know he's been re-united with his father at the British High Commission. I think we have got to recognise the exceptional role played by Greater Manchester Police and thank the Pakistan government.
"This is a co-ordinated effort to help a young boy, only five and separated from his family and now reunited with his father.
"People, of course, are very, very happy that this potentially tragic story is ending in Sahil coming back to our country today.
"We will be offering our good wishes to the family.
"It's obviously been a very anxious time for everybody and the whole country has been following this sad episode, where a five-year-old to be separated from his family is really a very terrible experience.
"We have got to have some understanding of what people have been going through, particularly Sahil, who hopefully will get back to enjoying his life."
Some of the kidnappers were "perhaps known to the family", a Pakistani government official said today.
Wajid Shamsul Hasan, the Pakistani High Commissioner in London, told Sky News: "This is what the authorities and investigators in Pakistan believe.
"The people that have been arrested in Pakistan, they must have known the family well.
"They have had some kind of grudge against them which is why they kidnapped the child and tried then to blackmail the father."
Pakistani police arrested a number of people after Sahil was taken.
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