The person was diagnosed with the infection - influenza A(H1N2)v - as part of routine national flu surveillance after visiting their GP in North Yorkshire with breathing problems, it is understood.

The person involved is not known to have worked with pigs and has fully recovered.

The source of the infection is still unknown and under investigation.

The UK Health Security Agency (UKHSA) said it is monitoring the situation closely and is taking steps to increase surveillance within existing programmes involving GP surgeries and hospitals.

There have been a total of 50 human cases of influenza A(H1N2)v reported globally since 2005; but none of them are related genetically to this strain.

H1N1, H1N2 and H3N2 are major subtypes of swine flu A viruses in pigs and occasionally infect humans.

Based on early information, the UKHSA said the strain detected in the UK differs from recent human cases of H1N2 elsewhere in the world, but is similar to viruses in UK pigs.

Meera Chand, incident director at UKHSA, said: "This is the first time we have detected this virus in humans in the UK, though it is very similar to viruses that have been detected in pigs."

Chief veterinary officer, Christine Middlemiss, said: "We know that some diseases of animals can be transferred to humans, which is why high standards of animal health, welfare and biosecurity are so important.

"Through our animal and human surveillance systems we work together to protect everyone.

"In this case we are providing specialist veterinary and scientific knowledge to support the UKHSA investigation."

Pig-keepers have been urged to report any suspicion of swine flu in their herds to their local vet immediately.

It is not known at this stage how transmissible the strain is or if there could be other cases in the UK.

It is also too early to say if the strain could have pandemic potential.

The UKHSA has notified the World Health Organisation (WHO) of the latest case.

In 2009, there was a pandemic in humans caused by flu strain H1N1, commonly referred to as swine flu.

This now circulates in humans seasonally.