City cars are the least effective in preventing whiplash in low speed rear end collisions according to a new study by Thatcham.

Fiat's 500 got a 'marginal' rating for safety. Two thirds of the supermini cars tested were rated as ‘marginal’ or ‘poor’. Renault’s Modus was the best smaller car with a rating of 'good'.

BMW's rating was the most improved manufacturer, having never previously achieved a ‘good’ rating. However, BMW has achieved a ‘good’ rating with its new 5-series, X3 and X5.

The full ratings, as well as video can be seen here.

Matthew Avery, Thatcham crash research manager, said: “City cars are not equipped to protect their occupants’ necks when they have to absorb the crash energy from larger, heavier vehicles.

“Although across the board we are seeing improved seat designs with around 75% of all new seats tested now achieving a good or acceptable rating, more can certainly be done.