Guessing here: a smart meter should retain much of the data it collects in non-volatile memory. A power cut should raise flags (start and stop) so that any data collector will know why data are missing from the sequence. I’ve no inkling of how a power outage would affect meters connected to off-grid sources - your PV array, for example. The meter will presumably continue to operate, though, whether that’s by its backup battery or (in your case) solar power.

I suppose it varies from collector to collector how they react to power cut flags, but I’m prepared to bet that it will take time for their data to look anything like normal again.

The Aclara SGM 1400 manual I referred to recently might help you fathom this out.

Yes, I realise that the data would be stored. It was just the ‘reaction’ to that for a few hours which I was wondering about and if the data collection point would indeed raise a flag. 
For solar PV, systems need an ‘islanding’ feature so that power cannot back feed towards any connected cables which are being worked on so unless there is a specific back up control for the system, it does not continue to supply the property 

The data is only sent once a day at midnight (or thereabouts, but not before), despite being collected throughout the day at your specified interval.

Thanks but while that’s right for the meter readings, the 30min slots are recorded more frequently hence the third party data apps can show progress during the day. 
Looking at the manual for the smart meter, it does log supply outages and highlights those over 3 mins in duration. Most DNO’s need to monitor supply locations to identify potential faults in action

@BPLightlog just checking that’s the answer, the clever smart meters are able to log outages that are over 3 minutes? 

I have a follow up question, I’m not sure how it works with energy generators like solar PV. When there’s a power cut, is solar able to power house appliances? Does it go to the meter, but not beyond it to the mains? 

According to the Aclara manual, yes. I know that DNO’s monitor areas to get advance warning of possible faults in progress

It really depends on how things are wired. Most systems need a ‘control’ feed to be able to both monitor and control but as I mentioned earlier, there are safety features installed which switch off the connection to the grid if a power outage is detected. 
Many do have an alternative feed system to continue supply for essential household items but most do not have this connected as it needs a separate dedicated wiring circuit with its own sockets