Warrington andy

Took my mk3 mondeo to national tyres to get the wheels tracked as I was getting some new tyres and there was a line of wear on the inside of both front tyres and the cord was starting to show.. Saying that I wasn't having any handling problems..everything was fine.. After I had the front wheels tracked on the way home the car was trying to Jerk left..I put this down to worn tyres and water on the road.. However I had 4 new tyres put on and the problem persisted..I took it back to national tyres and they were saying the tracking was way out but I only had it rectified 2 days previously.. I drove it away and instead of JerKing left and right occasionally it's now slowly veering left and right, occasionally..I'm sure they have done something in the garage that is wrong..has anybody else had any similar experiences and how did they rectify the problem please?