James Allen on Vettel's overtake

Ferrari want to establish whether there is enough evidence to lodge a protest that, if successful, could overturn the result of the Formula 1 world championship.

They are "evaluating footage" that appears to show Red Bull's Sebastian Vettel making an illegal overtaking move in Sunday's Brazilian Grand Prix.

Spain's Fernando Alonso lost the title by three points to his German rival.

But Vettel could lose four points if he is deemed to have broken the rules.

Formula 1's governing body, the FIA, has so far refused to confirm that it is investigating the incident.

There is no word either from Vettel's Red Bull team, who could not be contacted for a comment.

Final F1 standings 1. Sebastian Vettel - Red Bull 281 2. Fernando Alonso - Ferrari 278 3. Kimi Raikkonen - Lotus 207 4. Lewis Hamilton - McLaren 190 5. Jenson Button - McLaren 188

Video footage from Vettel's on-board camera appears to show him passing Toro Rosso's Jean-Eric Vergne in a yellow 'caution' zone on lap four of Sunday's race.

If that is the case and if any protest is made and upheld, it could result in a retrospective 20-second penalty for the German.

That would drop the 25-year-old from sixth to eighth, costing him valuable points and a third successive world title.

Alonso, who finished the race at Interlagos in second place behind Jenson Button, would then top the standings by a single point.

The 31-year-old Alonso, who was world champion in 2005 and 2006, is believed to be pushing Ferrari to make an official protest to the FIA.

However, the governing body does not need Ferrari to act to investigate further. In fact, its own rules appear to oblige it to do so.

Article 179b of the international sporting code says: "If, in events forming part of an FIA championship, a new element is discovered, whether or not the stewards of the meeting have already given a ruling, these stewards of the meeting or, failing this, those designated by the FIA must meet… summoning the party or parties concerned to hear any relevant explanations and to judge in the light of the facts and elements brought before them."

It adds: "The period during which an appeal in review may be brought expires on 30 November of the year during which the decision that is liable to review has been handed down, if that decision is likely to have an effect on the result of a championship."

That appears to give the FIA until Friday to resolve the situation one way or another.

Drivers must proceed with caution and overtaking is strictly forbidden in a yellow zone - indicated by yellow flags and flashing trackside yellow lights.

If a driver is caught overtaking in a yellow-flag zone, the punishment is either to drive through the pits at restricted speed if the race is still under way, or 20 seconds added to a driver's race time if the incident takes place close to the end of the race or is investigated after the race.

The footage in question was not shown on the main global 'world feed' during the race as it was showing repeats of the start at the time.

However, it has since been posted on the video-sharing site YouTube.

The video is now available to watch on the BBC Sport website and is embedded at the top of this article.

Vettel's road to glory in 2012

The footage shows Vettel passing two flashing yellow lights then overtaking Vergne down the straight, completing the move before reaching a flashing green light, indicating the end of the yellow zone.

Rules dictate that the 'yellow' zone ends only when the driver passes the first 'green' indicator.

Drivers are alerted to caution zones by an indicator on their car's dashboard display.

The yellow flag indicator in Vettel's cockpit is on the whole time.

If there is any discrepancy between what is displayed on a driver's dashboard and what is being displayed on the track, then the trackside flags and lights take precedence.

It is possible that Vettel thought he was free to overtake Vergne because he saw a marshal waving a green flag at the exit of the pit lane. In other words, before he made his manoeuvre.

A green flag is waved by a marshal at that post as Vettel passes the Marussia of Charles Pic on lap three, but it is not clear whether it was still being waved on lap four.

Some videos have appeared on the internet that seem to show an official waving a green flag but it is not clear on official television footage.

The likelihood of any protest being lodged or of any action being taken depends on whether Ferrari or the FIA can establish whether there was a green flag waving at that marshals' post at that time.

If there was, the case will be closed and no further action will be taken. If there was not a green flag, it is highly likely that the case will go before the FIA Court of Appeal.

Under a strict interpretation of the rules, the Court of Appeal would seem to have little option in that scenario to impose a penalty.

But it may well feel it has to evaluate how much of an effect on the result of the race a drive-through penalty for Vettel at the time would have had.

BBC Sport asked the FIA:

- If the stewards of the Brazilian Grand Prix had investigated the incident in question during the race.

- If there was a green flag waved on lap four at the marshals' post on the inside of the track after the exit of Turn Three.

- If the FIA was now investigating the incident.

The FIA declined to comment.