UK Car insurance law on third party stalling?

Ok, was in a car accident 3 months ago. was going onto a three pronged/t-junctioned roundabout and the car on the left pulled out and hit us. my insurance are telling me they can't defend me (i only have third party) until the third party insurance have given them a written statement. by the looks of things their client is refusing to write a written statement etc. the third party did send a witness statement about 3weeks ago to reply to but it was not for my accident. different location. so i don't think this is the insurance stalling. my question is does anyone know how long they can stall like this? the third party are trying to sue for injury as well and the guy gave a statement for that. claims we where going to fast and hit him on the white circle which i can prove wasn't the case as i have pics showing the glass is on the road. police attended as he flagged them down. he rang his mate to be witness and the police report shows dubious witness, flagged down and that they believe he didn't give way