The Williams-Renault driver will be Britain's first title-holder for 16 years if he wins the Hungarian Grand Prix, but his task has been complicated by the determination of the governing body, Fisa, to impose pump-petrol regulations. Mansell thinks his car, which runs on Elf, will be affected more than any other front runner.
Fisa, irritated by the failure of teams and fuel companies to agree on a new specification, says it found traces of 'power-boosting additives' in samples taken at the French Grand Prix last month - no names, no pack drill - and that it will take action if a similar discovery is made this weekend. The announcement has meant frenzied activity for Elf chemists and Renault engineers.
Mansell said: 'We tested with the new fuel at Silverstone on Tuesday and we were considerably down on power. Now we'll see who have the best fuel, because I'm pretty sure we had. Everything is going to be different.
'If anything, it has given me even more motivation to get the job done. I'm just amazed that the sport can be dominated by one team for four years with nothing set, nothing changed, yet all of a sudden this happens this year.'
The team he refers to is McLaren-Honda, who have been outclassed by Williams this season yet might now be able to close the gap, especially on this narrow, meandering circuit. They intend to try new cars equipped with active suspension in practice here, although they do not plan to race them.
Ayrton Senna may, however, be sufficiently encouraged to make the front row of the grid. Mansell's starts this season will scarcely fill him with confidence that he can take immediate command, even from pole position.
Mansell, 39 last Saturday, said: 'Qualifying is absolutely vital here because the race can be won and lost in the first five seconds.'
He speaks from frustrating experience. Last year Senna had the advantage going into the first corner and, for all the hounding of Mansell and his team-mate, Riccardo Patrese, would not relinquish it throughout the 77 laps.
Not that Mansell, who expects to race Renault's RS4 engine for the first time, ought to be under pressure to finish the job this weekend. He has a further five races in hand to eliminate Patrese and Michael Schumacher, of Benetton-Ford, from the contest.
Mansell maintains that securing the championship on Sunday would not accelerate a verdict on his future with Williams. Nothing, he says, has moved for six or eight weeks and is unlikely to for another week or two. He has stated his demands to Williams, no doubt attempting to protect his outright No 1 driver status. The arrival of Alain Prost or Senna would obviously compromise his position.
'I'm not bothered about Prost or Senna,' he said. 'I'm concerned only about my package. If we can reach the right agreement, maybe I can drive with one of them.'
Ferrari, competing in their 500th world championship event here, have named Senna as their No 1 choice for next season but have lined up his current team- mate, Gerhard Berger, as an alternative. Scuderia Italia, who use Ferrari engines, announced yesterday that from next season their cars would be built by the British Lola company.