HER house dates back to 1640, her office was created during the reign of Henry VIII and if this wasn't grand enough, I now have to remember to say "Hello Mrs Lane-Fox Pitt-Rivers" without getting it wrong, as Dorset's first lady Lord Lieutenant opens the door.

Before I can even finish she smiles and invites me: "Please call me Valerie, Val."

Val just doesn't sound respectful enough to the Queen's representative in Dorset, so I follow Valerie through an ancient stone archway into her cosy sitting room.

It's the first anniversary of her appointment as Dorset's Lord Lieutenant and it's been a busy year.

"I'm doing something practically every day of the week," she says.

The day before we met, she'd been escorting the Earl of Wessex to an event at Portland and the day after she was due to accompany the Prince of Wales to open the medical centre in Poundbury.

Minding the Royals is probably the most visible part of any Lord Lieutenant's work, but their duties are manifold - and unpaid.

She doesn't even get a dress allowance, just "a very nice badge".

If she'd been doing the job at the beginning of last century, Valerie would still have had the power to summon a militia. That power was abolished in 1921, but her office maintains strong links to the local military.

"Traditionally the Lord Lieutenant is president of some military charities and we are having a big do here for the Soldiers, Sailors and Airforce Families Association in the summer," she says.

(She and her husband, Anthony Pitt-Rivers, have a beautiful tithe barn which they allow charities to use for fundraising events.) Lord Lieutenants also maintain strong links to the reservist and cadet forces.

"All Lord Lieutenants love their cadets and every year you can select four who then become Lord Lieutenant's cadets."

They accompany her to events and she tries to ensure that each gets to attend a formal Royal visit plus other civic and military occasions.

Another of her duties is as Custos Rotolorum, a mouthful of a name for her responsibilities towards the magistracy as chairman of the Advisory Committees on Justices of the Peace and General Commissioners of Income Tax.

But it's the meeting and greeting side of her work she loves best and the opportunity it affords to "meet people and see what they're doing".

"You really do get to talk to people and see things you never would otherwise," she says.

"Anything I can do to help people to get their work recognised or celebrate what they're doing is marvellous."

She particularly enjoys being able to get organisations together who may be able to help each other, and passing on information about interesting projects for Royal visits.

"You meet marvellous people on Royal visits but you often don't get enough time to speak to them," she says.

She gets more chance when she is presenting a Queen's Award for Industry or for Voluntary Service, visits which take her all over the county.

"We had three companies receiving Queen's Awards last year - one of them was Reid Steel near Bournemouth airport and I found them absolutely fascinating, a delightful family business."

Does she always root for "her" Dorset and feel competitive about it?

"Oh yes!" But one thing she will have in common with all other Lord Lieutenants this year is that she is busy organising a service and tea party to take place in September to celebrate the Queen's Diamond wedding, in November.

"It will be a service to celebrate the sanctity of marriage with prayers for the Queen at Milton Abbey in the early afternoon with a tea-party afterwards," she says.

"The idea is that it will be a friendly occasion and anyone who was married on November 20, 1947 is very welcome to attend."

It's evident that planning this gives her great pleasure and, she says, she is looking forward to hearing "all the stories" that will be told about the historic day.

On a more sombre note she is helping organise an evensong at Sherborne in September, in memory of Princess Diana, who died 10 years ago.

So, is occupying a 500-year-old job quite what she had in mind when she left her native Yorkshire for London and joined an advertising agency?

"No! But I think it was good preparation."

During her time with the agency she worked on the Camay soap campaign, but gave it up after marrying Anthony Pitt-Rivers, descendent of the famous General Pitt-Rivers, the exuberant archaeologist and founder of the eponymous Oxford museum.

In combination with lengthy public service stints, Anthony runs the family farms and estate at Hinton St Mary near Sturminster Newton, where the family lives with Anthony's nephew, acclaimed event rider William Fox-Pitt and his wife and children.

When she's not Lord Lieutenanting, Valerie maintains a huge interest in sewing and embroidery - she is a former trustee and member of the council of the Royal School of Needlework.

And then there is always the domestic stuff.

Valerie Pitt-Rivers may be off to accompany the heir to the throne tomorrow.

But after I leave her she'll be off to the supermarket.

l If you are celebrating your diamond wedding on November 20, 2007 and would like to attend the day, please write to Marilyn Porter, Clerk to the Lieutenancy, County Hall Colliton Park, Dorchester, Dorset DT1 1XJ.