I have part exchanged my renault megane today for a picasso. Once all paperwork had been signed and completed i drove new car away. When i got home the garage called saying they wanted there car back as mine was faulty. The car was fine when i drove it there!! Do i have rights to refuse to take the car back and collect my old one as its not my fault something is wrong with it now. Should they have test drove it prior to any signing over anything and letting me drive the new one away? 
any advice?
any advice?