The group, proud of Birstall's "hidden gem" Grade I listed building, was formed after the hall and its gardens were refurbished and had its first meeting on September 11, 1988.

Now, honorary chairman Roger Knights says the group has evolved into something Kirklees could never have imagined.

He said: "In the beginning the hall had just been redone and the council wanted some community input. It's really just expanded from there.

"We now have 147 members working as a unit; a supportive working group. We have evolved into something quite unique in a lot of ways.

"We do everything, from building paths, taking trees down, giving advice, litter picking, building bridges. Anything that the ranger does really."

And what is the secret to the group's obvious success?

"We have a close relationship with the professional staff here," Roger said.

"We have a motto: We Trust Them. They Trust Us. And it's something which is very important. We have been very lucky in that they are very understanding, forward thinking people."

Another aspect the friends feel to add to their success is their offer to members of a vast range of activities and skills, both in the hall and in its gardens.

Roger said: "It's something we are proud of as a group and something we are quite famous for. Anything that needs doing at Oakwell we will probably at some stage be involved in it."

The friends keep their members informed of activities through a monthly newsletter which has won two awards.

The newsletter, first launched in July 1988, is printed by editor and membership secretary Lesley Hudson. It won the Liveliest Newsletter award from the British Association of Friends of Museums in 1998 and 2001, and was runner up in 2003.

But the highlight of the last 20 years was the visit to the hall from Prince Andrew in 2005.

Roger recalls: "It was unbelievable and all thanks to volunteer Beatrice Myers. At one of the committee meetings she mentioned the Prince had opened a doctor's surgery somewhere and so she was going to get him to come to Oakwell. She'd said she would write a letter.

"Three months later I got a frantic phone call saying 'he's coming, he's coming. What are we going to do?' We actually knew before the people at Oakwell knew but were told not to tell anyone."

Senior museum officer at Oakwell Eric Brown said: "We work with many different voluntary groups here but the friends help us in so many different ways. Their support is amazing and it is really appreciated.

"With the friends we have a wealth of experience and knowledge. Staff have come and gone for years but the friends are still going strong. It's only them who can write to Buckingham Palace and get not just a reply but a Royal visit! That was absolutely fantastic.

"They've had 20 fantastic, very successful years and are a wonderful group of people to work with.