Debrett’s thinks they understand modern etiquette. They don't, but thankfully I do...

People putting their dirty shoes on seats is just unacceptable. Get them off!

Research shows 45-55 year olds are the most polite (Getty Images)

When is it OK to light up your e-cigarette? If you are at work, the answer is never, according to Debrett’s, which has just issued a list of advice on etiquette for those anxious to get it right in today’s world. According to Debrett’s, people are now less concerned about thank-you letters and more worried about the vexed issue of when it is all right to recline one’s airline seat (never on short haul).

Well, as a one-woman missile for correct behaviour (I suspect this comes directly from being a mother-of-four, and I am unapologetic about it), I would like to give Debrett’s a bit of a steer. I have to say I am also aided in this by the stern forum that is Twitter, a fantastic place for pedants like moi who are always moaning like fury about things such as people who put their feet on the seats on public transport. So, shall we start with public transport?

Nearly 800 people wrote to Debrett’s asking whether you can indeed polish off a Big Mac on the train. The answer is no. Debrett’s now says it is not only bad form to eat on the bus, Tube, whatever (agreed), but that it is also off to put your make-up on when in a shared carriage, because it “makes you look disorganised”. What nonsense. I think actually it makes you look rather well organised, because you have thought about bringing your make-up (and a mirror) with you. Obviously adherents must be advised that nail varnish is always a risky business, and apart from that woman I was sitting behind on a Hull train the other day who sprayed her hair with dry shampoo, thus masking the entire carriage with noxious fumes, sitting quietly applying mascara is hardly antisocial.

Whereas people putting their dirty shoes on seats is just unacceptable. Get them off! “Could you please take your shoes off the seats?” I say to people, to the horror of my children. And while we are on the subject of public-transport etiquette, loud music on personal stereos is also a complete horror. I ask people to turn that down, too. Pretend I am worried about their eardrums. (As if.)

A new and rich seam for Debrett’s is obviously mobile-phone use. Apparently, more than 700 people contacted the publisher to ask about the etiquette of the smartphone. “It is always rude to pay more attention to your phone than a person in the flesh,” thunders the publisher, which was founded in 1769, quite a few years before the world’s first Nokia. Correct. It also says it is bad form to use your phone in the theatre or cinema. Also correct. Is there anything more obnoxious than some character in the row beside you switching on their phone and tapping away at that illuminated screen while you are trying to focus on a play?

During a performance of one play I went to last year, I was so infuriated by someone five rows below me continually working on his BlackBerry that I searched him out in the interval, marched up to him and told him off. At a later date, I also told off some people who were sitting next to me during a rendition of Bach’s The Well-Tempered Clavier by the great Daniel-Ben Pienaar, who started passing notes to one another just after the famous C major opener. “Guys!” I hissed, loudly, giving them a death stare. Although, as they failed to return after the interval, I may have inadvertently ruined their night. Whoops.

Direct intervention is, however, not always advisable. Turning round to disagree with an elderly man who was eating a large cheese sandwich in a vast plastic wrapper during a recital of Bach (yes, him again) by the wonderful Feinstein Ensemble, I was later introduced to him backstage by leader and soloist Martin Feinstein. “Please meet my father,” he said. I was speechless. “Actually a little part of me was rather happy,” confessed my husband, who is familiar with my intolerance. “Serves you right.” The trouble is that once my brain focuses on someone eating a cheese sandwich, or listening to music, or sniffing, then what I am meant to be focusing on goes out of the window, and I just start listening to the goings-on in Row C.

Other recent correspondents to Debrett’s included people anxious about the minefields surrounding when to kiss people (Debrett’s: not on first meeting. Millard: do it if it feels right, whenever), how to pour drinks (neatly, I suspect), and when to give up your seat (basically, when you see someone who needs it). Phones, cigarettes, meals, seats: this is what people are worried about these days.

Apparently, back in 2004 people were more worried about what to wear to Ascot, and back in 1994 correspondents were anxious about how to write to a titled person. I would say this represents a positive democratic shift.