Mr Bridges admitted that the blunder meant there had technically been no speed limit on a number of roads for up to 11 years. "Of course, that is not going to be the legal position because this law change will be retrospective," he said.
So far, just one local body, the Kapiti District Council, was confirmed to have expired speed limits. Mr Bridges said up to 25 councils might be in the same situation.
"We can be almost certain it's more than Kapiti District Council. How many and who, I cannot say."
Under law changes made more than 10 years ago, councils were given responsibility for setting speed limits on all roads except those with 100km/h limits.
These included roads outside schools where the speed limit dropped to 20km/h and stretches of highway where drivers were forced to slow down as they passed through townships.
Councils had to review their speed limits every five years or they expired.
Kapiti council officials approached the Government a month ago, saying they were concerned that its speed limits might have expired and other councils might be in the same position.
"They had a legal responsibility to review those within five years and then a grace period of two years and that didn't happen," Mr Bridges said.
In 2012, Auckland Council introduced a bylaw that amalgamated the speed limits set by the seven territorial councils that merged to form the Super City. It is unclear whether any of those seven had failed to conduct a speed-limit review.
The Labour Party's spokesman on transport, Phil Twyford, said that given the number of councils likely to be affected, the number of invalid speeding tickets could be in the tens of thousands.
Mr Bridges said: "We don't know how many but clearly a considerable amount of infringement notices ... have been issued and we couldn't have the legal uncertainty that goes with that."
Over the past five years, the total number of speeding tickets issued on all roads nationwide ranged between 50,000 and 80,000 a month.
The minister said the Government's top legal experts looked at a range of options for resolving the issue, but it was decided that retrospective legislation was the only way to fix it.
Why have some speed limits expired?
Since 2004, councils have been responsible for speed limits on all roads except state highways with a 100km/h limit. Because of a legal blunder, many councils forgot to renew their speed limits after 5 years, meaning they have expired.
What is being done about it?
Government was changing the law urgently last night to validate any speed limits set since 2004, and also any speeding tickets issued over that period.
What does this mean for tickets issued by these councils?
The tickets were, until last night, believed to be invalid. But the rushed law change will now make them valid.
