Has the work (£3000) been done yet?
If no then try and get your money back.
No you can not sue for repair , when buying a car it is always "Buyer beware".
As for the MOT , it is only good as the day it was passed by an inspector. If however you could prove that the car was unsafe when you bought it then you may have a case against them. ( to prove that you would need to get an independant inspection , someone like the AA, but you would have to pay up front , and if the inspection did not prove the car was faulty at the time of the MOT then you have no case and an inspection fee to pay).
PLEASE NOTE, if your car has been designated "unsafe to drive , then you may not drive it as it will invalidate your insurance. If you really like the car and dont mind spending money then get thework done by someone else , clearly do not goback to the original dealer. Good luck.