A director of the government's test and trace programme in England has issued a "heartfelt" apology for problems with the coronavirus testing system.
In a tweet, Sarah-Jane Marsh explained it was the laboratories, not the testing sites themselves, that were the "critical pinch-point".
This comes as scientists have sounded the alarm about rising coronavirus cases.
A new Lighthouse lab is due to open in Loughborough in about a fortnight.
Health Secretary Matt Hancock said there had been a "a problem with a couple of contracts" which would take a matter of weeks to be "sorted in the short term".
But he said he had "already put in certain solutions" to make sure people didn't have to travel more than 75 miles for a test.
Ms Marsh works as a deputy to Dido Harding, heading up the "test" element of the test and trace scheme.
The programme aims to find coronavirus cases through testing and, once confirmed, track down their contacts and tell them to isolate, in order to contain the virus.
Some people with symptoms have struggled to access testing in recent days, raising concerns these efforts will be hampered.
"All of our testing sites have capacity, which is why they don't look overcrowded," Ms Marsh explained.
Instead, appointments were restricted because of a blockage in processing capacity in the labs.
Carly in Manchester was left "angry and disappointed" after she tried to book a test for her seven-year-old son, who had a fever and a cough.
"I tried 30 or 40 times before I was able to get through and then I was told there were no appointments.
"At every point I was told everywhere's rammed to capacity."
But when she did manage to get a space at a testing centre at Manchester airport, she says there was "absolutely no-one there".
Some found the option of applying for a home kit was unavailable, only to be offered a drive-through testing appointment more than 100 miles from their home.
Rachel from Cardiff was directed to Dundee, more than 300 miles away, when she tried to apply for a test for her two sons, who had developed bad colds including symptoms she feared could be coronavirus.
She wasn't given the option of a home test.
Gavin on the Isle of Lewis in Scotland was directed more than 450 miles away to Portadown in Northern Ireland.
The BBC revealed the government was reducing the numbers of tests available in some parts of the country in order to make enough available where there were outbreaks.
Following this, Mr Hancock pledged that no-one would have to drive more than 75 miles for a test from Friday 4 September.
He told the BBC there had been "operational challenges".
In Parliament on Tuesday, he said: "I appreciate that 75 miles is far longer than you'd want to go and the vast majority of tests are much closer than that."
There have been suggestions some of the reduced capacity is down to schools in Scotland reopening, causing additional demand for tests.
This could worsen as term has started for chiRead More – Source