The Security Industry Authority (SIA) has apologised for the "poor service" provided for processing licence applications of pub doorstaff.
This follows reports in the MA of long delays for processing licence renewals in particular.
However, the SIA warned that some delays would still occur.
A statement on the SIA's website says: "There have been delays in our processing of licence applications and it has been difficult to get through to our contact centre. We apologise for the poor service."
The SIA blamed the "late delivery of a new computer system, combined with various administrative difficulties as we changed from a sub-contractor in Newcastle to one in Liverpool".
It also blamed postal strikes and the "flood of calls and e-mails" that followed issuing of more than 10,000 letters to doorstaff who were suspected of being illegal immigrants.
"The overall effect of all this has been a huge overload on our contact centre in recent weeks."
The SIA said extra staff have been drafted in to deal with the backlog.
"Any new applications (including renewals) will be scanned onto the system and will appear on the application status checker within a week of being received.
"Supporting documents will be returned within a further week, and the cases should then pass reasonably quickly through to the 'Checks in Progress' stage.
"In applications with a routine Criminal Records Bureau check and without overseas criminality checks, licence decisions should be made within six weeks of receipt of a correctly completed application form.
"Unfortunately, it will be some time before the load of telephone calls on the contact centre eases. Please do not add to the problem by making multiple calls or sending multiple letters or e-mails."
The SIA added: "Again, we apologise for the poor service provided in recent months. We have already cleared the delayed clearances in licensing, although it will be some time before all these cases are finally decided.
"Similarly, we anticipate the contact centre situation improving steadily as the new arrangements take effect and as the level of calls drops off."