Adblue problem - car smoking

Hello, I’ve tried to search for this problem I have on my 2016 DS3 1.6 blue HDI but can’t find anything. It has been such a great car and not a single problem since I got it from new but last weekend as I was driving suddenly it was blowing white smoke. I stopped and it reeked of ammonia and liquid was dripping out of the exhaust, presumably adblue.
I called the RAC out who said he had seen this a few times on older citroën Adblue models. He said it’s an adblue issue and will need to go a garage. I got it towed to my local garage I always use and they said they don’t touch adblue problems.
I have now booked it in at Citroën in a few weeks time but they are 15 miles away, I’m not sure if my car is safe to drive there. I’m a bit worried that it’s going to be a very expensive job and from past experience these problems seem to come back sooner or later.
Has anyone else had the same problem?