dodgy trader

Ok i bought a car less than 4 weeks ago was told that its a great car should fly through mot with little problems.
Upon doing mot yesterday the tester said that the car is a death trap and i should take it back to the trader i bought it from he also stated there is a marker for a serious accident on the vsi v40? so ive looked into it and the car was in an accident back in 2006 cat c, ive told the guy i bought it from ive been advised to return the car and get my money back he said theres no chance im getting my money back because he claims he didnt know about the accident and for me to take it in to him and he will investigate it.

Anyone know where i stand with this as im now without a car and im not even sure if its going to be safe after he has sorted the failures on the car any help would be appreciated

thanks