Farah, who had been due to compete in the 1500m at the Sainsbury’s Grand Prix in the Alexander Stadium, admitted yesterday that the controversy over last week's BBC Panorama documentary - which contained allegations that his coach at the Nike Oregon Project, Alberto Salazar, and training parter Galen Rupp had breached anti-doping rules – had “affected” him.

There were no allegations involving Britain’s 32-year-old world and Olympic 5,000 and 10,000m champion, but he expressed anger that his name had been “dragged through the mud” and said he needed to find out whether the allegations were true or not.

"This week has been very stressful and taken a lot out of me," Farah said in a statement.

"I have not been able to focus properly on today's race and after the events of the last few days feel emotionally and physically drained.

"I want to run well in the IAAF World Athletics Championships in Beijing and have decided it is better for me to go back to the US, seek answers to my questions and get back into training.

"I apologise to the people who bought tickets to come and watch me race and ask for your understanding at this time."

A stride after the line, however, the Londoner collapsed, holding his right hamstring, and was carried off the track.

There will be natural anxiety within the British camp over his fitness for a summer season leading towards the IAAF World Championships in Beijing from August 22 until 30.

Bracey’s winning time was 9.93.

The outstanding event of the day, however, was the men’s javelin, where Yego’s final effort was initially deemed to have finished outside the landing area but then deemed valid after officials had extended the line of the sector to make certain.

The judgement offered Kenya’s Commonwealth champion – who had walked the length of the field to confer with the judges – the ninth best throw of all time, and a dramatic advance upon the national record of 87.71m he set in Rome on Thursday (June 4) in finishing second to the 88.14m achieved by the Czech Republic's world champion Vitezslav Vesely.

After that second round flourish in the Stadio Olimpico, Vesely sat out the rest of the competition and nearly regretted it as Yego produced his outstanding effort in round four, and Walcott reached 86.20m with his last throw.

Today’s competition was totally different for the Czech, who was down in eighth place until he took the lead with a massive effort of  88.18m  in the last round.

Job done?

Not quite, as Yego stepped up to produce a throw that now stands just behind Britain’s Steve Backley in the all-time world list.

Olympic 200m champion Allyson Felix was narrowly defeated by fellow American Jeneba Tarmoh, with both being given a time of 22.29.

Britain’s Olympic, European and Commonwealth long jump champion Greg Rutherford rose to the occasion by winning with an effort of 8.35m, equalling his second-best ever.

In the meantime, it has been reported that the IAAF are concerned that media coverage of doping, such as the recent BBC Panorama programme, can risk undermining its own investigations.

An IAAF spokesperson said: “There have been allegations against the Salazar group for at least two years now and the IAAF has remained consistent in stating that it will never deny or confirm that it was undertaking an investigation into allegation of doping by athletes or supporting personnel.

“This is for obvious reasons.

"By confirming that an investigation is going on before it is complete is risking the efficiency of said investigation by tipping off those being investigated.

"The IAAF shares the USADA [United States  Anti-Doping Agency] point of view that attempts to sensationalise and publicise what are confidential and process-driven inquiries can end up ruining a lot of careful, painstaking work to uncover doping practices in sport.”

A statement issued yesterday by the World Anti-Doping Agency indicated it was the responsibility of the IAAF and the USADA to investigate the allegations.

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June 2015: Gatlin beats Bolt’s meeting record with 9.75 at IAAF Rome Diamond League
June 2015: Nike defends Mo Farah's coach over BBC documentary doping allegations
June 2015: Mo Farah's coach Alberto Salazar and training partner Rupp accused of doping
May 2015: Ibarguen, Lavillenie and Barshim are head of the field at Eugene Diamond League