Latest figures published by Applus, the organisation behind the national car testing programme show that 51% of cars failed their NCT in the six months to the end of June.
822,668 cars took the initial test with 399,704 first time passes and 419,905 fail refusals. 3,059 (4%) were classed as fail dangerous, which means that they should not be driven on the road. 418,334 cars were presented for re-tests and 380,505 (91%) passed.
It is thought that stricter rules regarding NCT certification and penalty points will lead to a record number of tests being carried out in 2015.
The primary reason for test failures are, front suspension, headlamps, tyre wear, brake lines and stop lamps.