Boris Johnson’s partner Carrie Symonds has made her first public speech since moving into Downing Street last month.
She gave a short address to the Birdfair environmental event at Rutland Water Nature Reserve.
Ms Symonds is also due to join a question and answer session with Chris Packham, presenter of BBC Springwatch.
She quit as director of communications for the Conservatives last year and is now a senior adviser for US environmental campaign group Oceana.
The 31-year-old works with the charity’s marketing operation in London and a profile on its website describes her as being “passionate about protecting the oceans and marine life”.
‘Glastonbury of bird-watching’
In her speech Ms Symonds said she was a newcomer to bird-watching, having become interested after visiting a puffin colony at Bempton in East Yorkshire.
She said she had been alarmed at seeing a picture of a slaughtered bird in a newspaper shortly afterwards, and condemned the trophy hunting of puffins.
Ms Symonds also referred to the “catastrophic levels” of plastic pollution in the oceans and said politicians and industry had a gigantic responsibility to care for the environment.
But she was “profoundly optimistic”, saying those who cared for the environment, particularly the younger generation, were in a majority.
She also referred to people’s description of Birdfair as being the “Glastonbury of the bird-watching world”.
Ms Symonds wore a floral print sustainable dress to the event.
The £225 garment is reported to be eco-friendly, having been made locally in London from a cotton blend that is biodegradable and which does not contain microplastics or dyes that pollute the environment.
More than 24,000 people attended Birdfair last year over three days.
Tim Appleton, founder of the annual event for birdwatchers, said it has raised £40m for global conservation projects in the 31 years that it has been running.
He said: “We’re absolutely over the moon that Carrie is supporting us and we hope she will continue supporting us and conservation for many years to come.”