Neal and Nandani were granted temporary visas

Neal and Nandani Nagla were allowed back to the family home in Ilford, in the London Borough of Redbridge, after being granted one-year visas.

While parents Lata and Aakash Nagla are British, under UK law the surrogate mother, Mrs Nagla's mother, is the legal parent.

The Naglas may have to adopt their own children to guarantee them citizenship.

Mrs Nagla cannot carry children because of a rare condition known as Rokitansky syndrome, but her eggs were fertilised in a test tube using her husband's sperm.

She looked for a surrogate mother in the UK and India without success before asking her mother Rhadha Patel, 44, who initially refused but later changed her mind.

These types of cases are not common Home Office spokeswoman

Fertility treatment was carried out in the western Indian state of Gujarat and the twins were born six months ago.

Paternal grandfather Natu Nagla told BBC London: "We were elated, we were really happy that finally God had listened to our prayers."

The twins have now been allowed back to the UK after lengthy negotiations involving lawyers, Ilford MP Mike Gapes, the Home Office and the British Consulate in India.

But the unusual nature of their case has stretched British surrogacy laws which say they are not automatically recognised as British citizens.

A Home Office spokeswoman said: "These types of cases are not common."

The Naglas may now have to adopt their own children in order to get them recognised as British citizens.

Or they could seek a parental order under the 1990 Human Embryology and Fertilisation Act.

Once legally recognised as the parents, they could apply for citizenship for the children after they have lived in the UK for a qualifying period, a process which could take five years.