A ferment in the world of the haiku - the 17-syllable verse seen as the simplest and most perfect form of poetry - will reach a head at a festival of 100 worldwide scholars in London and Oxford in August.

More prosaically, the controversy will reach down to touch the classroom lives of tens of thousands of British schoolchildren.They are encouraged to write haikus as part of key stage three of the national curriculum.

The form has broken free from its origins in classical Japan to be widely used in education, as well as by amateur and professional poets.

At stake in the controversy - argued over in documents thousands of words long - is whether the brief poems should emulate the rural calm of Mensuo Basho, 17th century Japanese father of the genre:

Waterjar cracks:
I lie awake
This icy night

or reflect modern realities, like a new haiku composed in Slovenia:

spring evening -
the wheel of a troop carrier
crushes a lizard

or one written by a computer games-playing US teenager:

Today I own you.
Tomorrow I will be ruled
The bloody wheel turns

The experts will also debate whether contemporary haikus should stick to the 17 syllable rule or be restricted in their number of lines.

The British Haiku Society has already begun rewriting guidelines in its 2,000-word pack for teachers.

Its president, David Cobb, reportedly said yesterday that the aim was to breathe fresh life into the form without trivialising it.

"One walks a very sticky path between elitism and populism. I would be very unhappy if we were the cause of the dumbing-down of the haiku," he said.

The present guidelines show how far English haikus have departed from their origins. A verse by Mr Cobb sticks closely to them:

the frost holds:
Friesians in the byre
chew steam

but another has only four syllables:

puddles
bubble.

The ferment began last September with the 4,000-word Matsuyama Declaration in Japan urging poets to "broaden the possibilities of a rich array" of diversified national versions for the haiku.

The declaration said even the traditional line arrangement - a single vertical line in Japanese calligraphy, three lines in the west - could be varied.

One of the poets who engineered the declaration is Susumu Takiguchi, organiser of the British festival. Mr Takiguchi, chairman of the World Haiku Club, writes sometimes traditional haikus from the peace of a farmhouse near Bicester, Oxfordshire:

spade splits the Earth
into two worlds -
earthworm in between

Yesterday he was enthusiastic about the "strong haiku movement" in the whole of former Yugoslavia, which wrote about violence and ethnic cleansing.

But he said the festival would challenge an American influenced "minimalist" trend towards single-line haikus which groped for "a moment of enlightenment" in the style of Zen Buddhism.

Replying to purists who insist on strict adherence to ancient Japanese rules, he added, "Diversity and difference do need to be encouraged."