For hundreds of years, Debrett’s has guided Britain’s aristocracy through the niceties of meeting royalty, going to the races or eating soup in the correct way.

Now the publishers of the bible of blue-blooded behavior are straying into previously unmentionable areas of the life of a modern girl — with a new book offering guidance on adultery, toplessness and celebrity gossip.

The first edition of Debrett’s Peerage and Baronetage — known in Britain as the “toff’s bible” was published in 1769, and its tome on manners, Debrett’s Correct Form, has guided high society for decades.

But according to its editor, Jo Aitchison, the new book “Etiquette for Girls” is a sign that the traditional arbiters of civility are catching up with the times.

“It’s a nod to the modern day,” she told Reuters. “We’re pulling Debrett’s out of Victorian times and trying to make it relevant to today.” The book’s advice ranges from how to conduct a sleaze-free office fling or a disease-free one night stand, to how to smoke at social occasions and what to do when you meet a celebrity.

But Aitchison insists the book is not all about sex, lies and partying. The core values of Debrett’s remain — elegance, composure and dignity are all important, whether you are dining with the Queen or cheating on your husband.

As well as advice on affairs, Aitchison points out that the book also includes suggestions on less risque subjects: How to behave properly on the way to work — “don’t sit on the bus and bellow down your mobile phone” — and what to take to a music festival — “earplugs and a pillow.”

Don’t be seen chewing gum whilst riding bitch, topless.