Was thinking about the starting point for this problem an hour or two ago and wondering if mud/carp from the water I drove through could've dried in the alternator causing a problem. Took a hose to it for a couple of minutes then with an extension lead used a hair dryer to dry it out for another five mins. Re attached battery making sure connections good and tight.
Battery light vanished as soon as I revved car and on checking with multimeter I'm getting 13.7 coming through and over 14 when revved.
A member has offered me an alternator which I'll be buying tomorrow if alternator reverts back to no charging tomorrow on the work run. Unorthodox solution if it has fixed the problem, and with any luck £400 + cheaper than the new alternator I was offered on Friday!