The Lady Guide to Modern Manners: 24 August

I went to a party recently given by an arts centre to celebrate its 25th anniversary and got an awful shock to find that my ex-husband was there with his new... what would you call her? I don't want to be rude... 'lady friend'. I didn't know what to do. I was completely flustered. If I'd had a pair of scissors... On the other hand, maybe it was best that I didn't. What do you advise?

Patsy Gilliat, Roehampton

Dear Patsy,

In an ideal world, this nasty situation ought never to have arisen. If it had been a private party the hosts should have warned you and your ex-husband of each other's likely presence. Then you'd have had a choice to stay away or go, and there would have been no risk of a nasty surprise.

In this case, it sounds as if your ex-husband ought to have realised that you would be there and either have stood down or come alone. Evidently he didn't, which is probably the reason why he is your ex-husband.

Certainly you are by sovereign right the wronged woman. But how to capitalise on it? Good manners, which at times fade to unwholesome conformity, decree that you must behave immaculately. The smooth, joyful purr of social life must on no account be disrupted. Other guests cannot be upset by the sudden bearing of varnished claws.

Yet people love a drama. And you might not be able to help it. How far can etiquette carry you? Christie Brinkley, a model of today, leant over to her ex-husband's new squeeze with utmost tenderness: 'When you find out he's cheating on you, I'll be there for you,' she soothed. This has a delicious ring of truth, for indeed a man who has cheated once...

The put-down path must be travelled with aplomb. Once you have delivered your lethal blow, metaphorically kick out your train as you swivel around and process away – ideally before loathed new girlfriend has had a chance to think of a half-witted reply.

Alternatively, you might prefer just to ignore the couple, which should be possible to bring off unobtrusively in a large crowd. To cut anybody dead at a party is downright rude, but in these circumstances, understandable.

The third approach, which might have an off-putting 'counselling' aura, so sensible it's boring, is to 'healingly' reach out to the new girlfriend. After all, you've got the awful man in common. Overdoing it ('Please be my new best friend') will look desperate, but civility, neutral topics, and light interest such as you might show to anyone newly met, can do no harm. Indeed, many ex-wives say it is ultimately less corrosive and more therapeutic to make the best of their replacement, especially if this woman is likely to have a certain amount to do with your children.

Please send your questions to Thomas.blaikie@lady.co.uk or write to him at The Lady, 39-40 Bedford Street, London WC2E 9ER.

WHAT TO DO ABOUT... admitting you're wrong

In the issue of 27 July, I attacked the Olympic organisers for too many bossy instructions (Boris Johnson's horrible automated announcements to bus passengers in London: 'Don't get caught up in traffic jams'). But the minute the Olympics started it was a different story.

The opening of the Paralympics is an ideal moment to mark that London 2012, in addition to the brilliant sporting achievements, the remarkable opening ceremony, the superb organisation, has also seen British courtesy and good manners reach a new pinnacle. Olympic volunteers have been friendly and helpful without fail, the soldiers and security personnel cheerful and unintimidating and perfectly natural, dignified and unprogrammed. The crowds at the venues have offered heartfelt support to Team GB. No hysteria or loss of control and a civilised willingness to recognise sporting excellence from other countries.

There has also been hearty singing of our national anthem, such as has not been heard for many a year. Our athletes have delighted and touched us with their modesty, dedication, and lack of interest in money and celebrity of the usual tawdry kind