Usain Bolt shrugged off the news that five Jamaican athletes have tested positive for a banned substance to win the 100 metres at the Aviva London Grand Prix.

Bolt was only second in his heat but powered to victory in the final ahead of compatriot Yohan Blake and Antigua's Daniel Bailey.

A headwind of 1.7m per second in the home straight at Crystal Palace ruined any chances of a truly fast time, but the world record holder still delighted a capacity crowd - including a large Jamaican contingent - with victory in 9.91 seconds.

Britain's Simeon Williamson was fourth in 10.19secs with former world record holder Asafa Powell back in sixth.

Asked about the positive tests, confirmed by the IAAF, Bolt said: “My friend called me and told me some tests were positive but I'm not worried.”

Speaking about the race, Bolt said: “Overall the main aim for me was the first 50m and I did well, I got it right so I'm happy.

“I knew it was going to be a headwind so I wasn't worried about the time. I got a good start, the transition was good so I'm happy with myself.

“I'm still at 85% (fitness) and after this it's all training, I've got two or three weeks of good training to put in so I guess I will be 100% by Berlin.”

Mo Farah failed to break the 27-year-old British record for 5,000m, but did at least win his race in a time of 13 minutes 09.14 seconds.

Dave Moorcroft's record of 13 minutes 00.41s - a world record at the time - has stood since July 1982 and Farah was always up against it with a strong headwind on the home straight.

“It was pretty windy but I just wanted to win if I couldn't run a time and I'm really happy with it,” Farah said.

Earlier in the competition, Britain's Nicola Sanders continued her return to action following a lengthy injury lay-off by winning the 400m.

Sanders, a silver medallist behind team-mate Christine Ohu

ruogu in the last World Championships in Osaka, has been struggling with an ankle injury but produced a gritty display to win in 51.54s.

“I was knackered coming into the home straight but I'm pleased with the win,” admitted Sanders, who just held off the American pair Shana Cox and Monica Hargrove.

“It just gives me confidence and I need wins more than anything at the moment.”

Pole-vaulter Kate Dennison broke her own British record four the fourth time outdoors this season, improving it by 1cm with a clearance of 4.58m with her third attempt.

However, she then failed with her three attempts at 4.68m, the height at which Olympic champion Yelena Isinbayeva entered the competition, although the Russian only cleared it with her final attempt and finished second on countback to Poland's Anna Rogowska.

It was a first defeat for the 27-year-old world record holder in a major event since the 2003 World Championships.