Conservative chairman Francis Maude has apologised after hundreds of people had to queue for hours to get into the party's conference in Bournemouth.
Some of those hoping to attend the conference waited for hours
Mr Maude told the BBC: "I apologise unreservedly. It's been a nightmare."
Tory officials were unable to say how many people had to wait to collect their passes or get late accreditation.
Mr Maude said the fact there were 2,000 more people attending - and tighter security after the August air terror allegations - contributed to the waits.
He held an emergency meeting with police on Monday evening in an effort to sort the problems.
Tory representatives grew increasingly restive throughout the waits.
One exhibitor on a stand with the Association of School and College Leaders said: "I'm hacked off. I sent in an accreditation form three months ago.
"My secretary was told on Friday that I still hadn't been positively vetted. I find that amazing. I'm an ex-colonel in the army and I have been to Tory party conferences before."
Another queuer said: "I'm an exhibitor and I've spent a lot of money to be here. I arrived from Belfast this morning and all the time I'm waiting in the queue, I can't be exhibiting."
Alix Blanchard, from Twickenham constituency, said she expected to be waiting for two hours.
"I don't understand it - I sent all my stuff off in July and they were quick in telling you that if you are late you will have to pay extra," she said.
Spotted in queues
A regional development agency representative said: "I was told it was going to take two and a half to three hours.
"At Labour it was all chaotic but I'm not sure what the problem is here. Maybe it's people applying late. In my case, the pass hasn't turned up at home."
Those wanting to collect passes ordered in advance of the conference were given cinema-style numbered tickets and ushered into an auditorium at the Pavilion Theatre to wait for their name to be read out.
Children's Commissioner Sir Al Aynsley-Green, Liberty director Shami Chakrabarti, former women's cricketer Rachael Heyhoe-Flint and several MPs were among those forced to wait.
And environmental campaigner Zac Goldsmith missed a speaking slot at a conference fringe event when he was delayed.
Mr Maude said he had visited the accreditation centre himself to "bang heads together".
"I hope to God it's sorted," he said after one official spent more than an hour reading out the names of 1,600 people who had now been approved for passes.
The tighter police checks involved telephoning people who had countersigned application forms and refusing to allow in people whose pass photos were not clear enough, he said.
Earlier, Mr Maude told those waiting to get into the conference that he was disappointed the police had not worked through Sunday night to clear the backlogs.
"I am incredibly sorry people are having to put up with this," he said.
"There is a big backlog of people's applications going through the police security process.
"We are going through them as quickly as we can. Any applications which are straightforward will get done, I hope, in the course of this morning, certainly in the course of the afternoon if not.
"The police have agreed to put more resources into it.
"They worked all through the night the night before last, not through the night last night, which was disappointing."
But assistant chief constable Adrian Whiting said Dorset Police officers worked until 0300 BST on Monday and extra officers have been drafted in to help.
"Dorset Police very much sympathises with those conference visitors who have as yet not been issued with their security passes," he said.
"We very much appreciate how frustrating it is to experience a delay in gaining access to the party conference."
Mr Whiting said the police relied on applications being sent from Conservative headquarters in "good time".
The vetting team had been available to issue passes from May 2006, he said.