Sir Christopher Chope dealt a blow to campaigners after announcing he objected to the Voyeurism (Offences) Bill that would make it illegal for offenders to take a picture under someone's clothing without their consent.
The Government stated its support for making upskirting a specific criminal offence hours before Lib Dem MP Wera Hobhouse's Private Members' Bill received its second reading in the Commons on Friday.
It was the crucial backing campaigners – including victim Gina Martin, 26, and her legion of famous supporters – were hoping for after months of campaigning.
But the Bill was scuppered by veteran Christchurch MP Sir Christopher, despite the best efforts of Ms Hobhouse to get him on side from the backbenches earlier in the session.
Theresa May has tonight voiced her disappointment at the Bill being blocked.
She said: "Upskirting is an invasion of privacy which leaves victims feeling degraded and distressed.
"I am disappointed the Bill didn't make progress in the Commons today, and I want to see these measures pass through Parliament – with Government support – soon."
It means the Bill will have to return for another Friday Private Members Bill session, on July 6, if it is to have any hope of becoming law in this Parliamentary term.
BLOCKED: The Private Members' Bill was scuppered by Sir Christopher Chope
“I am obviously extremely upset and disappointed that Sir (Christopher) Chope decided to object on this vitally important Bill for the women of England and Wales”
Even then, it would only take one dissenting voice to again put a stop to its progress.
Justice minister Lucy Frazer said the Government "has every expectation" upskirting will eventually become a criminal offence anyway.
Labour's Dawn Butler called on Mrs May to show leadership by making it clear "there's no place in the Tory party for Christopher Chope".
Home Office minister Victoria Atkins, also minister for women, and Tory MP Will Quince (Colchester) were among those who said "shame" when the Bill was blocked.
Moments after blocking the Bill, Sir Christopher also opposed Finn's Law – Government-backed plans to give police dogs and horses extra legal protections from attack.
In a statement, campaigner Ms Martin said she had spoken to Sir Christopher, who agreed to discuss the Bill with her.
She said: "I am obviously extremely upset and disappointed that Sir (Christopher) Chope decided to object on this vitally important Bill for the women of England and Wales.
"I remain positive, though. We knew this was a risk – but I now stand with powerful, passionate women and men behind me, and I am confident that (junior minister) Lucy Frazer is committed to – and will – close this gap in the law.
"I'm positive and hopeful that he (Sir Christopher) will become a supporter."
A Government spokesman said: "This behaviour is a hideous invasion of privacy which leaves victims feeling degraded and distressed.
"It cannot be tolerated, so it is absolutely right that the Government supports this Bill to make 'upskirting' a specific offence.
"While we are disappointed this Bill did not pass second reading today, we look forward to supporting these measures through the House at the earliest possible opportunity."
Richard Burgon MP, who backed the Bill, wrote on Twitter: "Disgusted to see that Tory MP Christopher Chope blocked the Bill in Parliament today.
"Labour have supported this campaign from the start, it's time for the Government to bring legislation and not rely on Private Members Bills, which their own MPs have undermined."