I have seen a short film which starts with (I think) a set of dominoes
falling and starting the next one falling etc. This leads to ever
bigger things falling over, including buckets spilling pools of petrol
and candles falling into them which start a fire which burns a cord
which releases a ball which spirals down a helter-skelter which knocks
a boat which sails over a pool of water..........

You get the idea?

The whole thing lasted about 20 minutes and was, I think, silent
except for the noise of the things falling, burning, dropping etc.

It gave the impression of being filmed in one shot, or at most in a
few long shots, and was absolutely magical - as I remember

What was the film. 
Who was the director
Most important - is it available in any format?

Hello icent,

I have seen this film and it is called "The Way Things Go" by Swiss
artists Peter Fischli and David Weiss (1987).  It runs for about 30
minutes and is available in a variety of formats and sources I have
listed below.

I saw this video in an art exhibition, so it had underpinnings in the
theme it was presented in, but judging by viewer's reactions it has
many effects.  There are candles, balls, boats, and flammable liquids
like those you listed as well as many other household objects:  there
are tires, barrels, wood planks acting as levers, and balloons.  It is
a very exciting to watch as the concept is a Rube Goldberg-type of
chain reaction, though (and this is key) without any apparent reason
(i.e., it doesn't help feed a baby at the end as a Goldberg cartoon
might).

The scenes take place a large warehouse and have only an ambient
soundtrack of the objects interacting with other.  It appears that the
entire film is one shot, but there are subtle cuts usually when the
camera zooms in on mist or fog (though I distinctly remember at least
one obvious cut which made the entire film quite profound if they
didn't try to masquerade the entire film as one shot).

There are three screenshots of the film at the Contraption website:
http://www.core77.com/contraption/may_99/

Rotten Tomatoes has a collection of reviews from the Washington Post,
and The Onion AV Club:
http://www.rottentomatoes.com/m/TheWayThingsGo-1087453/reviews.php

The film is widely available and I'd suggest taking a look at your
local library or art gallery to see if there is a version you can
borrow for free.  However, there are many sources to purchase the
film:

Amazon.com has the VHS version for $19.95 USD, though there are two
used copies for $15.00 USD (you used the term "petrol" so I took the
liberty of searching Amazon U.K., but they do not stock the video)
http://www.amazon.com/exec/obidos/ASIN/6304551630/104-3122579-9971136

First Run Features has a DVD version for $19.95 USD:
http://www.firstrunfeatures.com/vid/waydvd.html

DVDReview says the DVD version has bibliographies and biographies on
Fischli and Weiss:
http://www.dvdreview.com/news/PokeNews.asp?news_id=4710


Enjoy the film, igent!
carwfloc-ga


Search strategy:
Google:  "the way things go" fischli
Personal experience

This is superb. I have been trying to track this down for years, and
this has achieved it in 30 minutes. I am dumbfounded, amazed,
awestruck - and also delighted.

Thankyou, whoever you are.

Thanks for asking the question, icent-ga . . .  we saw that film years
ago, and it's a classic in our household.  But like you, didn't have
any idea of where or how to find it.  This "Google answers" thing may
be terrific for certain purposes!