Question Author
Thanks all.
I did think about the insecure WiFi as, when I tried to access another website I was presented with a warning to that effect.
I've run through the troubleshooter provided by Zacs. None of the strainghtforward solutions have worked and it's getting very involved, suggesting "Repairs" and reinstalling Office. I'm sure that can't be necessary as it was working perfectly at home. I've an idea it's something to do with the WiFi here but I shan't spend too much time on it as I'm only here for a week!
Thanks again for your help.