Our national obsession with antiques underpins the huge success of the BBC’s Antiques Roadshow and its many spin-offs. Today, Kate Ironside and her sister Virginia are appearing on BBC2 in a special edition of Celebrity Cash in the Attic

VIRGINIA had a problem. My half-sister, 60s rock columnist, agony aunt and author rolled into one, had been invited to appear on Celebrity Cash in the Attic.

She'd accepted, but it wasn't that simple.

"Darling…" she cried down the telephone, "I have to have a friend, someone to react with! You'll be my friend, won't you?"

Absolutely. But what did I have to do? I hadn't a clue.

I am appalled to say that, until that day, I had never actually watched Cash in the Attic or its Celebrity spin-off – a function perhaps of being a working mother with two small children who regard the television remote control as their own private property. And, delightful as the programme may be, it does not have the same appeal to the junior Ironsides as Basil Brush or Prank Patrol.

Some homework was required.

Cash in the Attic's formula is quite simple. Accompanied by the presenter and an expert, the participants rummage frantically around their homes for objects worth selling. Once the expert has identified a clutch of saleable items, the cast moves on to the auction house, where the bidding begins.

Within half an hour or so, the participants, or, in the case of the celebrities, their charity, are either thousands of pounds better off or, um, not.

Virginia's charity was Hope and Homes for Children, which provides vital support to children caught up in conflicts round the world and which also has played a major part providing alternative homes for those tragic children imprisoned in cots in East European orphanages.

Cash in the Attic becomes in its own way compelling viewing. Its success is rooted in the nation's utter fascination with antiques. Or, to be blunt, with treasure.

That is the bottom line. While some of us may be genuinely entranced by 1920s glasswork, 18th century furniture and all the sophisticated odds and ends in between, the real draw of these programmes is the eternal appeal of the treasure hunt.

Will the participants find something genuinely valuable lying neglected and overlooked in their attic, their garage or even in their garden shed, or is what they own merely trash? Will they, at auction, raise the fortune of their dreams? Or leave empty-handed?

It's easy drama… but not easily produced.

The first day's filming took place at Virginia's house. I arrived to find her looking marginally alarmed, her home taken over by a small army of young men whose jeans hovered precariously at their hips.

They sported clipboards, cameras, tripods, microphones and endless mugs of tea.

"There's an old colleague of yours here," Virginia hissed, stretching it a bit. "Someone from the Western Morning News."

At which point the programme's presenter, Angela Rippon, emerged from a clutch of cameramen, plunging straight into warm reminiscences of her early days working in the photographic department of the Western Morning News as a teenager.

"The bell used to go off and the presses would roll – it's not the same any more…" she recalled wistfully.

But there was no time for more recollections. We had a programme to film. Throughout it all, Angela was the consummate professional.

As ever in television the best spontaneity is well-planned. Virginia had already decided – and found – what she wanted to sell before the crew bowled in.

This was partly because they were on a tight schedule and partly because Virginia, an avid collector of paintings, clockwork toys and all sorts, was determined to decide quietly by herself, in advance, which of her precious possessions to give up.

The only point at which I spotted her elegant hackles rising was when the director, departing from the script, suggested she threw in a painting that she had only just bought at auction.

Much of what Virginia did decide to sell was from the 60s – memories of the days when my father used to step over me crawling along the floor to yell up the stairs: "Virginia, there's a Paul McCartney on the phone!"

The chief prizes which excited the amiable expert Jonty Hearnden were a book signed by John Lennon and a set of photographs by David Bailey that included both the Krays and Lord Snowdon.

But, for the sake of the cameras, we had to find them first.

Virginia rummaged. Jonty rummaged. I rummaged.

I was repeatedly filmed rifling through Virginia's cupboard under the stairs and extracting from alongside the mop, the WD 40 and the damp sealant, a trio of pretty berets that had belonged to her fashion designer mother, Janey.

What a surprise to find them there!

Angela was the glue that held the programme together, keeping the story of the hunt going… "What's this you've found Kate? Now tell me, Virginia, about …."

Huge efforts were made by the crew to conceal from us the final total of what the expert Jonty thought we would raise.

"It needs to come as a surprise to you," explained researcher Ben – a surprise we then had to re-enact twice as the director demanded retakes of the moment the news was broken to us.

But there was no scope for retakes a week later when we went to Chiswick Auction Houses in London for the sale.

This was genuine live action – the auctioneer rattling through an impressive array of lots.

If the crew missed a bid, that was it. It was gone. The pressure was even more intense. They were also filming the auctions for three other editions of Cash in the Attic. The crews were juggling like madmen.

When the bidding began, Virginia, the presenters and I were parked in a corner of the room. Some lots sank without trace but at least for two we had rival bidders on the phone in different sections of the room. This was the moment in an otherwise sleek, well-planned production which was genuinely unpredictable. It was utterly gripping.

Did Virginia raise her total? That would give the game away.

You'll have to watch to find out – 5.15pm on BBC2 this afternoon.