On regular drive from Edinburgh to Newcastle (area) this morning I drove the first 60 miles without problem.
Stopped for coffee at services then carried on when battery/ignition warning light came on.
After a short while I became aware of a regular ticking noise which got steadily worse and seemed to match engine (or travel) speed.
Sounded to me like a possible fan belt issue.
Pulled in to next services and called out Ford Assist who sent me an AA patrol.

He checked belts, as OK, checked charging on idle and load and suggested a possible alternator malfunction. 
Took it for a short drive which showed the faults to have cleared.
His advise was to get home and take it straight to dealer to have further investigation to the alternator.
Drove the remaining 70 miles with no further problem.

Now, I've booked it in with my Ford dealer but can't get an appointment for over a week which gives me time to make other enquiries.
If it is the alternator I should be covered on my Gold Warranty but if, on investigation, the problem has cleared then I may be charged for diagnostic time.
Any ideas or suggestion as to what it may be would be helpful as all now seems good.

I am a 2011 Fiesta Titanium 1.4 auto with 62000 miles, regularly serviced by Ford dealers.

Just to follow up.

Last 3 days, running around town, no problems.
The issue seems to have cleared. I would have thought that short stop/start journeys would show up any trouble with alternator or charging.
Still wondering if anyone has ideas as to what may have caused this as I am reluctant to pay for investigations which may prove fruitless.

Sounds like alternator clutch pulley might have been slipping.  Very odd that its been fine ever since though.  Unfortunately it's probably one of those things that won't be easy to diagnose until it gets worse or at least constant.

Thank you .... interesting!

Going to keep running over the weekend before I decide whether to get things checked or not.

Update in case anyone had been watching this.

Eventually managed to get booked in with my Ford dealer. They checked it out and found that it was, indeed, a faulty alternator.
Now alternator and ignition coil being replaced under the Ford 2 year warranty that I got when I bought the car 18 months ago.
Pleased I didn't have to shell out. Now able to save up for timing belt replacement which is due in a couple of months!