Against my better judgement...

[evdama]

decades ago I jump started someone's car for them and it damaged mine somehow.

Never Again I vowed.
Until today I had to start my stepdaughters Zafira.
No problems until a few miles into the return journey ,a bleep and the battery light on the dash.
Turning off then back on clears it but it's back on again a few miles later.
Because it's temporarily ok I'm guessing it's not a fuse
Got codes relative to the BSI
U340A (F40A)
U18D5 (D8D5)
U35FF (F5FF)

Edit
Just done a bsi reset
Now I have no power steering and STOP on the dash
Any Ideas where to start
Where's Sol when you need him!

[shtu]

F40A is bogus, that;s the oil level sensor not being given 4 or 5 months to decide what the oil level is.
U35FF is probably related to a BSI reset being done incorrectly.
U18D5 is one that neither google or i recognise.

Clear them and start over. eg, check the fuse that serves the power steering pump.

The alternator issue is quite likely to be the slip rings worn out. Easily checked. If the charging voltage is fine initially, then suddenly stops charging, only to return when you restart, quite likely to be that.

[Multispacer]

decades ago I jump started someone's car for them and it damaged mine somehow.

Never Again I vowed.
Until today I had to start my stepdaughters Zafira.
No problems until a few miles into the return journey ,a bleep and the battery light on the dash.
Turning off then back on clears it but it's back on again a few miles later.
Because it's temporarily ok I'm guessing it's not a fuse
Got codes relative to the BSI
U340A (F40A)
U18D5 (D8D5)
U35FF (F5FF)

Edit
Just done a bsi reset
Now I have no power steering and STOP on the dash
Any Ideas where to start
Where's Sol when you need him!

I would try disconnecting your battery, removing it and putting it on charge overnight. Some error codes can get held in memory even after a BSI reset but leaving the vehicle with the battery disconnected for a number of hours [ie overnight] means that any memory circuits will be completely discharged and will revert to default state.

[evdama]

Thanks chaps
I disconnected the battery for the last few days as a means of preserving charge while I get chance to look but there's no change
The codes are all in the bSi section of the diagnosis
I've cleared them but they return.
All is absolutely fine for 5 mins then the issue kicks in
Much as I hate ai Google suggested a multimeter on the battery- 11.8v resting and 9.75v running - the alternator is a distinct possibility.
75 k on the clock is perhaps a bit early for wear- I don't know -but it's too much of a coincidence that it's failed immediately after this
The Mrs ,feeling partially to blame has phoned a garage who said the same and she booked it in.
Electrics are not my bag so I have agreed to it as It would probably get more expensive the more I experiment.

[Multispacer]

Thanks chaps
I disconnected the battery for the last few days as a means of preserving charge while I get chance to look but there's no change
The codes are all in the bSi section of the diagnosis
I've cleared them but they return.
All is absolutely fine for 5 mins then the issue kicks in
Much as I hate ai Google suggested a multimeter on the battery- 11.8v resting and 9.75v running - the alternator is a distinct possibility.
75 k on the clock is perhaps a bit early for wear- I don't know -but it's too much of a coincidence that it's failed immediately after this
The Mrs ,feeling partially to blame has phoned a garage who said the same and she booked it in.
Electrics are not my bag so I have agreed to it as It would probably get more expensive the more I experiment.

Looks like your alternator isn't charging. I suspect the diode pack might have blown on the alternator [that's the electronics that converts the AC to DC] In the past you could get replacement diode packs but everyone justs wants to sell you a new alternator nowadays.

[shtu]

Much as I hate ai Google suggested a multimeter on the battery- 11.8v resting and 9.75v running - the alternator is a distinct possibility.

That probably explains the lack of power steering, that's "lucky it runs at all" voltage levels.

[evdama]

It was a butt clenching ride home.
Took it in for repair early doors this morning.
I had the battery leads off over the bank holiday and a trickle charger on the battery.
Started in ok and no lights on the dash
Bloke did a diagnosis and couldn't find any issue and. >14v on the battery
Hopefully that had allowed it to reset itself

I should be over the moon but  I'm not  going to celebrate until it's had chance to play up
I don't trust it with no closure.
I am partially interested to see if the fault codes have clears but I'd only stress out of they havent

[evdama]

Knew I should not celebrate
Battery light back on.
It's fine intermittently.
I've noticed that even when it's ok,the battery warning lamp that's lit on the first key position will flash before going out.
Against my experience I have started down the road of buying parts to experiment.
I've ordered a new batter,as it's the easiest and cheapest first item.

[evdama]

New battery fitted 
doesn't flash battery light on 1at key position
Battery light back on after 20 mins
Booked into specialist week next.

[shtu]

It's almost certainly the alternator, and most likely the slip rings.