Cash-strapped Rover, which is locked in partnership talks with a Chinese company, saw its new car sales slump last month.
A total of 6,608 Rover cars were registered in March 2005 - well down on the 9,247 figure achieved in March 2004, the Society of Motor Manufacturers and Traders (SMMT) said.
The MG part of the Rover business performed better, with sales rising slightly from 5,810 in March 2004 to 5,937 last month.
While MG's share of the market rose 2.19%, Rover's share slipped 28.54%.
Overall, new car sales in March 2005 - a new number plate month - reached 442,940, a 5.1% dip on the March 2004, but still the second-best March figure ever.
See Thursday's Birmingham Post for more on this story
The top 10 best-selling models in March 2005 were:
1. Ford Focus
2. Vauxhall Astra
3. Vauxhall Corsa
4. Ford Fiesta
5. Peugeot 206
6. Renault Megane
7. Volkswagen Golf
8. Renault Clio
9. Ford Mondeo
10. Volkswagen Polo