Major telcos are offering compensation to tens of thousands of customers for slow NBN speeds.

Telstra has admitted to the ACCC that it may have engaged in misleading or deceptive conduct and made false or misleading representations in NBN advertising that claimed it could provide download speeds of up to 100 megabits per second (Mbps), and maximum upload speeds of 40 Mbps.

Optus says it is “working with the ACCC… to provide appropriate remedies to those customers where it has been confirmed that the underlying NBN service cannot deliver the speed they signed up for”.

Australian Competition and Consumer Commission (ACCC) investigations have shown many customers are not receiving the high speeds they had paid for.

The regulator found the top speeds “could not be achieved in real-world conditions” due to limitations of customers' fibre to the node (FTTN) and fibre to the building (FTTB) connections.

“Our investigation revealed many of Telstra's FTTN and FTTB customers could not receive the maximum speed of their plan,” said ACCC chairman Rod Sims.

“Even worse, many of these customers could not receive the maximum speed of a lower-speed plan.”

The ACCC says around 56 per cent of Telstra’s FTTN customers (26,497 people) on the highest-speed 100/40 Mbps plan could not actually achieve those speed levels.

Over 9,600 customers in that category were unable to hit half of that speed.

Forty-five per cent of FTTN customers on the 50/20 Mbps plan were incapable of hitting full speed too.

Telstra has struck an agreement with the ACCC for remedies to affected customers.

They will be offered refunds, and Telstra will allow them to change plans or ditch their contracts without paying a fee.

Optus says it is considering a range of measures for customers depending on their individual circumstances.

TPG says it is in discussions with the consumer watchdog.

Dodo and IPrimus, both owned by Vocus, are working with the ACCC too.