The Princess raised a laugh as she congratulated organisers on their foresight in keeping the official plaque she was to unveil out of the wind and rain, under the cover of a marquee.

"Otherwise it would have been unveiled some time ago," she said.

The Hawk and Owl Trust education centre is a milestone in a £1 million investment in the reserve, boasting CCTV cameras trained on wildlife around the reserve, a classroom and displays introducing visitors to birds of prey and other wildlife at Sculthorpe Moor, as well as its history.

It was a return visit for the princess, who opened the reserve four years ago.

She said: "It's a real pleasure to come back and see just how much it has changed and grown. The advantage of having a proper education and information centre really does add to the potential of what you have here. That only happens really thanks to so many people contributing not just money but a lot of time and effort. Many thanks and many congratulations."

The princess braved the weather to see the developments outside the centre by walking along some recently-constructed boardwalk to its newest hide.

Throughout the visit she chatted to staff and volunteers who make the reserve what it is, as well as members of the trust's after-school Kestrel Club for eight to 12-year-olds.

Among them were Bethany Ellis (10), a pupil at West Raynham Primary School, and Megan Smith (9), donning birds of prey costumes to meet the princess, who asked: "You don't usually dress like this?"

President of the trust, actress Liza Goddard, was at the event with granddaughter Adelaide (7), who presented the princess with a posy.

Ms Goddard said: "I am full of admiration for someone who does this every day of the week and comes to it fresh and interested in what we do."

Ms Goddard's friend and former colleague TV actress Susan Jameson (Bergerac and EastEnders) was also there with comedy actor husband James Bolam, famous for his part in The Likely Lads.

Volunteers Debbie Mitchell, Chris Potter and Chris Wright, who attend the reserve weekly from the Elizabeth Fitzroy Support day centre in Fakenham, were among those who stood in the rain to wait to meet the princess.

Debbie said: "She was a nice lady. I didn't expect her to chat with us as well."

Volunteer Eric Adnams (73), of Norwich Road, Fakenham, met the princess again having seen her on the last visit when she was presented with a barn owl nest box. He said they chatted about the variety of nest boxes there are, adding: "She is still as nice as ever."

On leaving the centre, the princess signed the visitor's book, simply with "Anne" and the date.