I ran it and I managed it but I had not trained enough. I ran it in 97 minutes which is okay. The first 10km took me 42 minutes and it took me 55 minutes to do the next 11km. This makes it clear that I had not trained enough. Specifically at distances beyond 10km.
In Munich last year my second half pace was as good as my first. At least my training seems to have improved my 10km speed.
There were a few possible other factors influencing my slower overall pace. It rained the whole time and I had two pub crawls in Edinburgh Wednesday and Thursday. However, I think by Sunday it should have been out of my system. I think it is much better explained by weaker training. I intend to keep my fitness up and enter another half marathon soon.