Editor-At-Large: Janet Street-Porter

What do you think museums are for? Not a day passes at the moment without another tremor shaking one of these institutions to the core. Most recently it was the turn of the British Museum, which, having completed a hugely expensive rebuilding programme with the construction of the Great Court, now seems like a rudderless ship (one that's running out of cash).

Having visited plenty of museums both old and new, I can tell you exactly what they are for in the New Labour world of Accessibility and Education for all. Museums as currently approved and funded are simply repositories of artefacts grouped around a coffee shop and a load of computers.

God, how I hate the bloody smell of coffee. Why does it have to dominate everything, from the Wallace Collection to the National Portrait Gallery? The huge injection of cash into museums over the past couple of years has produced very little real benefit to anyone other than the owners of Costa Coffee, Justin de Blank, Starbucks and their huge band of consumers. If I were studying early English ceramics or the history of watercolours, I would find that my chosen areas of academic research would be as pathetically poorly displayed as before. Museums are now places to snack and shop.

The much vaunted extension to the National Portrait Gallery is actually a giant escalator that whisks you up to the floor below a brand new restaurant, with one of the best views in London. The main scholarly improvement is that the Tudor portraits have been brilliantly re-hung on grey tweed. The extension has also provided a new gallery, filled with the most appalling load of rubbish - late 20th century portraits of everyone from Zandra Rhodes to Joan Collins, executed by artists who aren't even in the third division of talent. Why they can't be replaced by a gallery of the true medium of late-20th century portraiture - photography - seems plain perverse.

The National Portrait Gallery has fine Victorian galleries, but when it comes to the present, standards seems to have gone out of the window. In the "learning" gallery beside the new escalator, a bunch of girls on a school trip were playing with the computers. They had called up a photograph of Geri Halliwell and were religiously copying it into their notebooks in pencil. If you're interested, there are great escalators at Selfridges, and a similar outlook is available while you drink at the View Bar in Leicester Square.

Both the Wallace collection and the British Museum covered over their courtyards so they could fill them with nasty chairs and sell coffee, Danish pastries and postcards. The hanging of the bulk of their collections remains unchanged. Next month I anxiously await the opening of the new British Galleries at the Victoria and Albert Museum, praying that it will not mean a larger coffee shop and extended gift area. I adore this museum, having spent months on its upper floors researching a book about the history of the English Teapot 20 years ago (I know: I've had an eclectic career). My only companions, apart from the odd museum attendant, were several plastic buckets and containers positioned to catch the drips when it rained.

The V&A is still bleating about raising cash from the government for a gaudy extension on the Brompton Road, designed by the great architect Daniel Liebeskind. But what exactly will go in into this extension? Why can't the V&A just content itself with displaying its collection better in the space it already has?

No wonder museums find it hard to get directors - they don't seem to understand their primary purpose: to be a centre for academic study. If you get the visitors, that's a plus. But history and design certainly cannot be explained through interactive gobbledegook and touch screens with pictures of Chippendale chairs.

Deep down, I think the Government will only be happy when all museums are geared towards 12-year-olds. You might find that rich, coming from the ex-High Priestess of Youth Culture, but I am astonished that so much store is set by appealing to the young in a cosy, non-threatening way. Why? Go into an art gallery in Moscow and you see school children on trips sitting in front of paintings while teachers talk them through it. Of course it might be boring for some, but so what? Why should art and history have to appeal to all? In the new Magna Centre outside Rotherham, millions have been spent transforming an old steel mill into a science museum. But you won't find the dreaded m-word anywhere, in case it puts the kids off. It's an Adventure, or even more patronisingly, an Experience.

The Magna Centre is brash, noisy and thoroughly interactive, and full of screaming, happy kids having a great time chucking water over each other. The section at the start, featuring the history of the area, is a slide show. Again we seem frightened of words, of content, of depth.

The new Tate Gallery in St Ives has been a huge success, and the current retrospective of work by the late Bryan Wynter is well worth seeing. This is a fussy, over-elaborate building, with the whole top floor given over to a restaurant, in a town full of places for a cup of coffee or a snack. On one level is a picture-free "learning area" with catalogues resting on a shelf under a window with a great view of the beach. The space for hanging pictures is relatively small.

Of course, building galleries for contemporary art is an easier proposition than re-hanging and refurbishing the old, and the results, from Gehry's Guggenheim in Bilbao to our Tate Modern, have been huge successes. But I make a plea to Matthew Evans, our Museums Tsar, to focus on all the unloved, untrendy and equally important smaller city museums around Britain. Let's not reduce our national arts heritage to a kind of New Labour cultural Complan, with kids' drawings stuck up in the foyer and espresso machines frothing away in the background.

Lose weight, ask me how

In a few weeks' time I shall be attempting to climb Mount Kilimanjaro, and I'm not at all sure that I'll make it to over 18,000 feet. So I've started the Street-Porter diet, in order to lighten my load. It involves spending an hour a day reading diets other people are on, eating regular amounts of meat, fish and vegetables washed down with medicinal quantities of red wine, and planning visits to a new gym. The benefit of this regime is that it keeps me far too busy to get on an exercise bike and read the ghastly Anne Robinson's memoirs each day.