This weekend's A1 Grand Prix meeting at Brands Hatch has been handed added significance with the decision to cancel the planned finale at the Autodromo Hermanos Rodriguez following the outbreak of swine 'flu in Mexico

World Cup of Motorsport organisers announced the decision as participant arrived in Britain for the annual trip to Brands, confirming that they had acted on the advice of the UK Foreign Office to cancel all non-essential travel to Mexico. The decision reinstates Brands Hatch as the scene of the 2008-09 showdown, having been supplanted by the desire to include a round in the Americas.

“To say we are disappointed to have to make this call is an understatement,” A1GP chairman Tony Teixeira insisted, “When the news of the health problems broke last week, we made sure we kept ourselves up to date with the latest information. It soon became obvious this was not an isolated health risk and, when the UK Foreign Office put out its advisory and the World Health Organisation raised the level of influenza pandemic alert, that was when we had to make our decision. We must have the safety of all members of the A1GP community, as well as the thousands of loyal fans in Mexico City, as our prime concern.”

The timescale between rounds also played a part in the decision to can Mexico, as air freight was due to be flown across the Atlantic directly after this weekend's Brands event, but Teixiera is adamant that the cancellation should not be seen as another potential nail in A1GP's coffin.

“If we had flown our cars out and not been able to send the teams to run them, it would have been a waste of time and money," Teixiera explained, "However, this cancellation does not impact on the future of the series and, once Brands Hatch is over, we shall be concentrating on season five, for which plans are already well advanced.”

Heading to what is now the final round, three teams - Switzerland, Ireland and Portugal - can still win the championship, and the battle is sure to go down to the wire as none of the tri can clinch the title in the opening sprint race.

As usual, the permutations are numerous and complicated, but the destination of the crown will be decided as follows:

Switzerland will win the title if both Ireland scores less than three points or Switzerland outscores Ireland by at least two points and Portugal scores less than seven points or Portugal doesn't outscore Switzerland by more than two points. If scores are tied, Switzerland needs to maintain its better tie-break results, which currently sees it have four wins to Ireland's three and Portugal's one

Ireland will win the title if it scores at least three points and doesn't lose more than one point to Switzerland and more than four to Portugal. If scores are tied, Ireland needs to have better tie-break results.

Portugal will win the title if it scores at least seven points and outscores Switzerland by at least three points and Ireland by at least five. Trailing Switzerland by three wins means that Portugal cannot beat the reigning champions on a tie-break even if it wins both races in the UK. If it ties with Ireland at the top of the standings, the number of victories will determine the champion but, with both countries possibly ending the weekend on three wins, the number of second places, then third places, etc will be used to determine the outcome.