Qualifying for the Sao Paulo Grand Prix was postponed until Sunday by torrential rain at Interlagos, but an even bigger storm was brewing off the track with governing body the FIA understood to be investigating allegations by Red Bull that McLaren are among a number of rival teams illegally filling their tyres with water to improve their performance.

The suggestion, which first surfaced in German publication Auto Motor und Sport and has been verified by Telegraph Sport, is that a number of teams, notably McLaren, have been injecting water – or another unspecified liquid – into their tyres through the valves shortly before they are fitted to their cars in the race. Doing so could keep the tyre cooler which would help to limit thermal degradation, and ultimately help deliver better race pace, particularly in the latter stages of the race. Or so the theory goes.

A technical directive was issued by the FIA a few years ago outlawing such a practice, with Red Bull among the teams thought to have used the technique in the past. The Milton Keynes-based team, who have lost a number of senior engineers to McLaren, now suspect their rivals of doing so, which they believe might explain their leap in performance. They also suspect other teams of having followed suit.

It is understood they became suspicious around the time of the Singapore race when water was seen emanating from a tyre when it was removed from the rim. They promptly raised the matter with the FIA, asking them to investigate.

Telegraph Sport has asked McLaren, who denied doing any such thing but declined to comment publicly. Tyre manufacturer Pirelli likewise declined to comment on the specific allegations but a spokesperson told Telegraph Sport that it would be “duty-bound to report anything illegal to the FIA” if it saw anything like that.

The row is the latest in a tit-for-tat war between Red Bull and McLaren which has raged all year, with McLaren’s “mini-DRS” rear wing and Red Bull’s “front bib adjuster” both coming under scrutiny. Both teams agreed to alter components in the wake of allegations, although neither squad was found to have done anything illegal.

Whether anyone will be found to have done anything illegal in this instance is uncertain. It will be difficult to prove anything retrospectively. Formula One tyres are all destroyed post-race. But if there was anything going on, it is likely to have stopped by now given the scrutiny.