Formula One returns to action in Spa this weekend after an unprecedented volume of contract activity during the summer break. Yet much serious business is far from settled – especially for the title protagonists, Lewis Hamilton and Sebastian Vettel, who begin a championship run-in likely to be decided by the finest of margins.

After Hamilton won in Hungary the curtain fell on a demanding first half of the season. At the time there were many ongoing driver negotiations but little was anticipated in terms of actual movement over the break. Five days later Daniel Ricciardo made the shock announcement that he would not, as had been expected, re-sign with Red Bull but was to join Renault for 2019.

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The Australian cited the desire for a new challenge but factors such as a lack of faith in Honda’s power unit for next season, his desire to be an undisputed No 1 driver and even perhaps Renault convincing him that their works team have championship-winning material in the pipeline, are all likely to have played their part. His move opened the floodgates.

Fernando Alonso then made his less unexpected statement that he was to leave F1 at the end of the 2018 season after 17 years in the sport, although he remains open to returning should McLaren make their way back to the front of the grid. Alonso will be greatly missed but, with the Indy 500 now his target and McLaren way off the pace, it was only a matter of time before he walked. With the market thrown open by Ricciardo, McLaren had to move and two days later announced they had signed Renault’s Carlos Sainz for 2019.

Red Bull, too, now had a seat available and they opted to stick with their method of promoting from within the ranks, taking Pierre Gasly from their sister team Toro Rosso for next season. Gasly celebrated, he said, by running round shouting in his pants before jumping into a swimming pool. A pleasingly enthusiastic response but Red Bull also know he is a strong asset. He brings knowledge of Honda’s power unit and this season where it has been strongest Gasly has delivered exceptionally well – fourth in Bahrain, seventh in Monaco and sixth in Hungary.

All of which had been preceded by the news that Force India had been saved from administration by a consortium led by the Williams driver Lance Stroll’s father, Lawrence. This was superb for the team, who have outperformed better-funded rivals and deserve to race on – but it further complicates the driver market. Stroll is almost certain to take his son to Force India, who are also likely to retain Sergio Pérez, leaving the Mercedes junior Esteban Ocon without a drive. He is now a contender to replace Stoffel Vandoorne at McLaren but they are also considering their junior Lando Norris, who will drive in his first Grand Prix weekend in FP1 at Spa. Williams in turn will have a seat open and a big Stroll-shaped hole in their finances.

Deals are still to be done then but at the sharp end these are the distant sounds of musical chairs, not a distraction for Hamilton and Vettel, embroiled in a fight as tight as either driver has yet encountered. Hamilton’s win over Vettel in Hungary, after his victory from 14th in Germany, has given him a 24-point lead over his rival. It is the greatest advantage either driver has held all season but is not indicative of how competitive their battle has been.

The Mercedes and Ferrari are remarkably closely matched and, with the Scuderia making a real step forward this season in power, the advantage Mercedes previously enjoyed on grunt‑dependent tracks has all but disappeared. Indeed, what the opening 12 races have indicated is that this title will be decided by the men behind the wheel and their team more than machinery.

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The Mercedes technical director, James Allison, pointed out after Hungary that only five races had been won by what was the fastest car and seven had gone against the head. “Small differences, maybe an error, maybe a moment of particular genius, or just sheer good fortune or ill fortune is what is determining who comes home smiling at the end of the race,” he said.

Luck, then, will play a part, as it did with the VSC and safety car in Australia and China. So will strategic calls, as Mercedes found to their cost in Melbourne, Shanghai and Austria, and both teams will require a bulletproof mechanical performance. Given all those factors so far and that Ferrari are now quicker in a straight line than Mercedes and hold an advantage through the slow corners, Vettel would have expected to be leading after Hockenheim and Budapest.

But in Germany his “off” in the rain cost him dearly while Hamilton’s superb drive there and his brilliant pole in the wet at the Hungaroring proved vital. As things stand, it is the drivers who look to be the crucial differentiator. Both are settled with their contracts and the next nine meetings will prove which one has really earned all those zeroes to claim a fifth title.