National WHAT?

I'm in a quandry. November 4th is United Nations Day, and Boy #1's school is putting on a show for parents, who are 'kindly requested' to attend. For 'kindly requested', read; 'you will be the worst parent in the world if you can't make it and your card will be marked not only at the school gate but in the class room at parent's evening as well if we don't see you there bright and early on the relevant day. But no pressure, of course...'

Obviously I would want to go in any case; Boy #1 has been practising renditions of 'The Hello Song' - no, I hadn't heard of it before, either - and 'We are the World' at the dinner table. Even without a tune, it's powerful stuff, I can tell you, and I will be stockpiling emergency tissues to stem the 'emotional mummy tide' well in advance of the great day. They've been practising hard, he tells me, and I can see that; so hard, in fact, that his throat was "really hurting, mummy" (assumes sad, tired voice), "and I really don't think I should go to judo today because the rough and tumble at the end won't do me any good at all..."(tails off into complete pathetic-ness).

Now, the quandry is not whether he should or should not have gone to judo. He didn't go, as it happens; his glands were swollen and I need him well tomorrow, so I decided to make like a panda and give in on this matter like a proper mummy for a change. That is, as opposed to the seargent major persona I normally adopt when a male member of my family is ill (it doesn't do to encourage them, what with their being the weaker sex and all).

No, the quandry is related to this part of the letter informing us of the United Nations Day Celebrations:

'Children should come to school in their National Costume...'

This is all very well if you have a national costume. In fact, it's all very well for probably the other 51 of the 52 nationalities attending Boy #1's school. But can someone tell me what the English national costume actually is?

I've been going through the options and they're not great...

Football / rugby kit in England strip. Not great, lacking in imagination, maybe slightly (whisper it) chavvy, but on the plus side easily obtainable.

Bowler hat and suit. No, don't laugh, looking at it from a non-Brit's perspective that seems to be what many people think is actually worn to work in the city of London. Thankfully however we posess neither a suit nor a bowler hat for Boy #1. Thankfully, in fact, we don't posess a bowler hat for any of us...

Morris dancing outfit. (Rationale for suggesting this is as above). And no, no, no and no. Aside from anything else, our stock of white handkerchiefs wouldn't stand up to scrutiny. Plus, white jeans in late Autumn? Darling, I think not.

Cricket whites. Could be onto something here - if it weren't in NOVEMBER. And no matter how Oxbridge he might look, I refuse to outfit my son in whites for a one-off event when we're off to the land and snow and ice, where cricket is about as common as marmite, in a few weeks time.

So please, help me out here. Anybody got any ideas that don't include any of the above or the final option; what seems to be the standard 'Brit abroad' uniform of crocs, an umbro t-shirt and a pair of three-quarter length jeans?