THE mattresses had probably been in service since the D-Day landings, but the sheets smelled of fresh air, and the eiderdowns were fluffy as a souffle. Arriving as a child at Mrs Potts’s honeysuckled cottage in deepest Selkirkshire was like the first page of a Famous Five adventure: full of promise, and designed to put you in the holiday mood. Even if my father had been sufficiently well-off to book us into the Ritz, he would have thought that a very poor second.

Mrs Potts offered breakfasts that would propel an Arctic expedition to the North Pole, afternoon tea to make the table buckle, and an evening meal that required a two-hour walk to digest. While I played with Sammy the cat, or picked strawberries, or paddled in the stream, Mrs Potts would come out to chat. During these weeks, her home became ours. There were no fire doors or smoke alarms, and Health and Safety might have frowned at the ginger tom prowling the kitchen. Yet, like all natural hosts, Mrs Potts knew what her guests needed and wanted, and took pleasure in providing it.

Even back then, hers was a rare place, of a kind already disappearing. Most of the B&Bs I later encountered were considerably less charming, ruined by nylon sheets and nicotine baths. But as tourism flourished, so standards in this, the lowest rung of the hospitality trade, greatly improved. Today, threadbare candlewick bedspreads or loo-rolls encased in crochet are more likely to be found in a museum than in any establishment that has heard of TripAdvisor. Of late, in fact, I’ve found one in the Borders that makes the most bijou hotels look dreary and uninspired.

It was with a pang, therefore, that I read of the travails of this crucial sector of our economy. Even though visitor numbers are rising, the humble B&B appears to be toiling. Figures from VisitScotland show that occupancy rates in cities and major towns have fallen by almost 10 per cent since 2001. Edinburgh has been worst hit, with a drop of around 17 per cent. Some of this is down to the arrival of budget chain hotels, whose attractions include not only the guarantee of uniform quality, but their useful central locations. With the ever-rising popularity of stag and hen parties, one can also understand why some guests might prefer their anonymity to returning, possibly worse for wear, to face tiptoeing up the stair in a house just like your mum’s.

The biggest threat to bed and breakfasts, however, comes not from hotels, but from Airbnb. This booming phenomenon, in which spare rooms are turned into piggy banks, attracts custom from the same folk who used to trundle their wheelie cases along those never-ending suburban streets where signposts hung from every other window like tea-towels out to dry. But these days there are no signposts. Your neighbour next door or upstairs could be renting out a room, or the entire premises, to strangers, making a profit with no more effort than a bit of hoovering and dusting. Tempting, isn’t it?

Originally, Airbnb’s ethos was appealing. Sharing your home occasionally for a brief spell and a skeleton rent seemed a clever way of benefiting others as well as yourself. In essence it was the same principle on which bed and breakfasts were founded. Now, though, thanks to social media and the internet, word of mouth has hit the fast lane, and recommendations fly thick and fast as midgies. Surely only the terminally old-fashioned or sour could find fault?

Perhaps – no, without doubt – I am both. If the young man across our landing lost his job and turned his flat into a revolving door of tourists, I would object, on the grounds of noise, neighbourliness and security. Yet increasingly it is not just the cash-pinched who are taking this route to make ends meet. Disgruntled B&B proprietors are beginning to jettison old-style habits and adopt this low-maintenance, cut-price model.

So too is that well-heeled breed who buy-to-let as a way of making more income. In a never-sleeping city like Edinburgh, the financial benefits of short-term lets over the long-term tenant have grown too enticing for the avaricious to ignore. I know of one rich New Town resident who bought a flat a mile or two away and renovated it for Airbnb. Within days it was fully booked for Hogmanay and beyond. Yet how would she feel if this carousel of tenants took up residence next to her? You don’t need Alan Bennett to write that script.

Where those in the traditional hospitality trade must abide by safety and hygiene regulations and inspections, Airbnb hosts are not bound by such rules. Horror stories, such as the flat whose balcony collapsed, or the owner whose home was trashed, are relatively rare. Nevertheless, they point to an intrinsic flaw: by avoiding red tape, those who make money through Airbnb can undercut traditional rentals.

There is no code of conduct, no professional oversight, and no guarantee that the room or flat or house on offer meets legal requirements. And in the long run – and perhaps worst of all – the race to make a quick buck is threatening to corrode the market for those needing rented accommodation, not for a weekend or fortnight, but for months or years.

It’s dispiriting that what began as a well-meaning project has so quickly been hijacked for self-interested commercial use. Unlike the days when Jim Haynes, one of the co-founders of the Traverse Theatre, published a list of “like-minded friends” around the world who would happily offer anyone a cheap room for the night, Airbnb has come to typify the hard-nosed, grasping end of the hospitality trade.

So it was with glee that I overheard an Airbnb landlord last week moaning to a friend in a cafe. He had walked into his Georgian living room one morning to find one of his tenants reclining on his sofa. Her husband was asleep, she explained, and she did not want to disturb him. I do not know in what terms he reminded her that she had rented the basement, not his entire house, but I wish I’d been there to eavesdrop. Mrs Potts, on the other hand, always welcomed me warmly when I drifted into her quarters, usually in search of the cat.