By Natalie Bennett

“There is a dead female rat in the square garden.
File it under SC MISC.”

That’s a recent short exchange from the readers’ comments book at the London Library. Unpick the terse phrases, and you’ll get to know a lot about this unjustly little-known London institution.

London Library readers, by and large, are the sort of writers who’ve checked their footnotes three times, who’ll never be caught out with a spot of inadvertant plagiarism in their latest book. So when they see a dead rat, they won’t just note its presence, they’ll collect all of the information they can about it.

The second line, translated, means “science, miscellaneous”. Not for this library the calm mathematical march of the Dewey system, but some glorious, madly illogical, and very, very 19th-century system of its own devising.

Look up “Korea” in the electronic catalogue and you’ll find nothing is under “K”. Most is in History.Corea (apparently the 19th-century spelling, or just what the librarian preferred), a monograph of incense burners under “Art.Bronzes”, Korean movies under “Science.Cinematograph”, plus a few books under “T” for travel.

It is a wonderfully mad system that I’m sure gave some 19th-century librarian a chuckle as he put Science.Witchcraft beside Science.Women. But it does, in its own way, work. Often, having trudged up the rattling staircases, scratched your head, and gone back down again, you’ll eventually find your way to the appointed shelf, and discover that while the catalogue entry that took you there turns out, in the cellulose, to be disappointing, nestling beside it is just the text that you need – or if not, then some irresistably titled alternative that will give you hours of reading pleasure – and pleasure that you can take home, and keep just like it was your own, for many a week.

It was this essential readers’ need, not just access to books, but access at a time and place of their own choosing, that led Thomas Carlyle in 1841 to found this institution – a lending library for the serious scholar. The British Museum reading room was impossible as a workspace he complained – a complaint with which many of resident of Humanities 1 in the new building in King’s Cross would have sympathy – and many of the luminaries of 19th-century London agreed. So it was that the first political economy section was selected by John Stuart Mill, Thackeray its first auditor and Gladstone was on the first committee. Other early members included Dickens and George Eliot

It started with 2,500 books, and in 1845 moved to the site it still occupies, in the north-west corner of St James’s Square, tucked slightly incongruously behind expensive tailors, more-money-than-sense restaurants and discreet watering holes of the London splasherati. (Although the Royal Academy is just across Piccadilly.)

The building was entirely reconstructed at the end of the century, producing in its reading room, with its plump leather chairs, wrought-iron galleries and soaring ceiling, one of the finest spaces in London. It also produced one of the most curious, the books stacks behind, with their grilled, see-through floors definitely not designed for the vertiginous. (And definitely not designed for heels – I’ve only worn them to the library once.)

Since that original building the library has grown and grown – now some 1 million volumes. It is primarily a humanities library, and what fiction there is by definition is supposed to be “literature”, although if you dust off a random volume of 19th-century “literature” — quite probably not borrowed since the year of publication — you’ll find that claims of literary decline would seem to be seriously overstated.

Almost miraculously, the library has managed to find space in this expensive bit of central London to expand, if in a fashion that has produced a complex layout that leaves many a new user bemused. And it is now expanding again, into a building known as Mason’s Yard, which will provide many facilities currently lacking, including an outside roof terrace, and vitally, bicycle parking, since Westminster Council, despite many pleas, has singularly failed to provide enough public spaces in the area.

So the London Library is emerging into the 21st century in fine fettle, even if, to judge from that comments book — which more regularly features laments about infestations of mobile phones and laptops than rodents — that century is little to the taste of many of its readers.

Membership of the library currently costs £210 a year, for which you can have 10 books out at any one time. (And there are no fines for overdue books – although you might get a sharp email from the librarian.) If you are visiting London four-month memberships are available for £110. Under 24s can be members for half the regular cost. At first glance that might look expensive, but when you think that many of the libraries scholarly volumes cost 60 or 80 pounds, and you can keep that volume for months, it is an extraordinary good deal.

Read more in the Telegraph (I think this piece is by Tom Stoppard, but it has lost its byline into a crevice of cyberspace; Antony Peattie in The Times.