The number of new cars licenced for the first time fell again in June, slipping 52.4 per cent.
Only 7,369 new private cars were registered in June, compared to 15,465 a year earlier. New goods vehicles also saw a decline, slipping 5.6 per cent to 1,181.
In total, 11,774 new vehicles were registered during the month, a fall of 45.1 per cent.
This is the fifth month in a row that the number of new cars registered has fallen. The most recent decline follows a fall of 39.8 per cent in May.
A new emissions-based car tax system that was introduced in July could be partly responsible for the decline in new car sales, as potential car buyers waited til prices fell as a result of the new regulations.
Meanwhile, first licencing of second-hand cars rose 6.4 per cent compared to a year earlier.
The total number of vehicles licenced in June fell 31.8 per cent to 20,007.
A research note from NCB said the fall in new car sales had been exaggerated by the strong performance seen in 2007 thanks to the maturing of SSIAs, but numbers were still trailing 2006 levels.
The director general of the Society of Motor Industries (SIMI), Alan Nolan, previously said that it was widely expecetd that the decline in sales seen in the May statistics would carry through to June.
However, NCB said that despite the predicted increase in sales in July as a result of the new car tax regime, sales for the year would still be "unlikely to impress", with car sales typically slowing in the second half of the year.