I solved this eventually. I firstly purged all urls in the joomsef control panel. Then cleared the JSef cache. Then cleared the JS cache in joomla under the tools menu (clean Cache). Then waited for the default cache time in joomla to be up - 15mins in my case although i gave it half an hour.

Probably a combo of logic and magic but seemed to do the trick.

Peter

Likewise - Since the most recent update 3.6.3 my site isn't creating new sef urls nor processing new 301 redirects.

Really urgent as i have made loads of amendments that are either not showing or throwing 404 - if anyone can give any insights as to what is happening i'd be supremely grateful!

P