The sporting "Crown Jewels" of English summer are facing pressure to scale-up crowd numbers significantly after the Prime Minister insisted he was "very positive" about the end of social distancing. A leading public health scientist joined industry figures in calling for Wimbledon and Royal Ascot, in particular, to abandon their "excessively conservative" plans following Boris Johnson's upbeat assessment. While Twickenham and Wembley plan to be at least half full by July, Ascot next month could be restricted to just 4,000 racegoers - seven per cent of its normal numbers. The All England Club is also currently restricted to 25 per cent capacity, despite beginning a week after the Government is due to release most restrictions. As Government last night formally enacted plans for 10,000 spectators to return from Monday, Professor Robert Dingwall, who sits on the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), suggested Wimbledon should be planning for attendances of up to 70 per cent. Describing current plans in racing and tennis as "excessively conservative and inflexible", he told The Telegraph governing bodies should be feeling emboldened. "There is a broad scientific consensus that outdoors is as near zero risk as any scientist will ever commit to, unless spending any length of time in a very crowded space with restricted air movement," he added. "Given this, I would have thought that large outdoor sports venues could be considered on a case by case basis - there aren't so many of them. Where you have a high proportion of spectators in open spaces, which would apply to large areas of most racecourses or the outside courts at Wimbledon, I would have thought you could have a high proportion of normal capacity - maybe 60-70 per cent rather than 25 per cent." The All England Club has stated that it is flexible in its arrangements, and insiders believe bigger percentages for Centre Court and No1 are all-but-certain by the end of the fortnight. Organisers of Ascot and the Epsom Derby are also privately holding out hope that the British Horseracing Authority is able to improve on its announcement on Monday that only 4,000 people would be permitted from May 17, including owners, media and racing staff. "Ascot could probably hold 80,000 - 4,000 is so so small," said Sam Hoskins, a racehorse syndicate manager who runs both Kennet Valley Thoroughbreds and Hot To Trot Racing. "We need the authorities to see that one size does not fit all. I just hope some discretion can be used because a lot of these big racecourses are very safe places." The Premier League, meanwhile, continues to lobby hard for guarantees on full venues by the start of next season. Richard Masters, the league's chief executive, said 10,000 at the final two rounds of the campaign will "ensure a fantastic finale to the end of our season", but he added: "We will continue to work with the Government and other authorities as our priority is to have full vibrant stadiums – including away supporters - from the start of next season. Only then will we get back to the real Premier League." As stadiums finally got the green light to reopen in bigger numbers than have been seen for 14 months, the Big Six club owners stood accused of failing to learn lessons from the European Super League fiasco. Supporters drew a sharp distinction between Burnley, who are giving more than 3,000 tickets away for free, and Tottenham Hotspur, who have set a price band of £60 for their only home fixture against Aston Villa. Malcolm Clarke, chairman of the Football Supporters' Association, told The Telegraph: "In general terms, it doesn't surprise me that Burnley are doing something decent - and it doesn't surprise me that the greedy six might not be doing something decent. We would welcome any club that recognises the sacrifices that supporters have made along with everybody else." Rugby Union is also pushing hard to increase crowd numbers, with hopes that England fixtures against USA and Canada on July 4 and 10 will be watched by a half-full Twickenham. Government confirmation that the nation is on track in its roadmap out of lockdown confirmed plans first set out on February 22. “We’ll unlock the turnstiles of our sports stadia subject to capacity limits,” the PM confirmed. Significantly higher numbers of spectators are expected from June 21 onwards. "I'm optimistic that things will get back much closer to normality, let me put it like that," said Mr Johnson, when pressed for further detail. "You'll hear a lot more by the end of this month about exactly what the world after June 21 is going to look like. At the moment, I'm feeling very positive about it, but we've got to be guided by the data." Government crowd pilots continue on Saturday when 22,000 people attend the FA Cup final between Chelsea and Leicester at Wembley. It emerged that the Duke of Cambridge will be on hand to present the trophy to the winners. However, despite the upbeat assessment from scientists and politicians yesterday, only one in four people are planning on attending football matches or music gigs as soon as restrictions allow, a survey suggests. The survey, conducted by Yonder, on behalf of leading Covid-19 testing company Cignpost ExpressTest, found around half would return to events if measures such as PCR testing, reduced capacity and social distancing, were in place.