Asked to supply a log cabin

More questions than answers I think.

Is this a single phase 100A supply ? Is there an obvious 'origin' CU feeding the others - so really it is 'container supply' or 'garage supply' or whatever that are 30A sub mains  feeding final circuit sub-boards at the  locations. or is it lots of boards on Henley splitters only fused at the meter tails level of protection ? 
The former would sound like an industrial spark used to big factories but working on domestics, and  may be OK if the final circuits have RCD cover, that latter would be a someone too tight to pay for a larger main board ;-) 

Agree, a quick tot-up of total loads to see if an upgrade is recommended, but there are plenty of flats with showers sharing fuses that give no issue, so it may be alright.
Does it look like things have been overheating or damaged ?

are there heavy loads ?

Do you want the aggro ?

Mike.
PS cheapest if slightly dishonourable  is to do your bit as another small CU, split at the meter  tails and say ' I'm leaving all that alone and not testing it ' to the existing rest of it.

Yes 100a main fuse supplying the property. 

There is a main cu withing the property which supplies other boards, but im sure it was like a cu will feed another one then that one would feed another one and so on.

Kind of dont want to get involved with testing 

 it was like a cu will feed another one then that one would feed another one and so on

Yep. that is someone used to industrial work, stick another DB instead of run more than one cable all the way back !

Mind you I can't really be too disapproving, I have a CU in the house one way of which is a 32A sub main that feeds a small DB in the garage, that in turn has RCBOs doing garage lights and power, and one more MCB way in that feeds an SWA submain that goes to the two sheds, each of which has small DB that splits the supply over separate power and lights RCBOs . It minimises the walk to reset things, and in practice has never tripped on anything that was not a real fault.
So I can sympathise. (quick sanity check is an IR test over the whole lot from the house CU end and R2 wander to verify as many far point earths as can  sensibly be reached and note the highest ... )

Mike.

 it was like a cu will feed another one then that one would feed another one and so on

Yep. that is someone used to industrial work, stick another DB instead of run more than one cable all the way back !

Mind you I can't really be too disapproving, I have a CU in the house one way of which is a 32A sub main that feeds a small DB in the garage, that in turn has RCBOs doing garage lights and power, and one more MCB way in that feeds an SWA submain that goes to the two sheds, each of which has small DB that splits the supply over separate power and lights RCBOs . It minimises the walk to reset things, and in practice has never tripped on anything that was not a real fault.
So I can sympathise. (quick sanity check is an IR test over the whole lot from the house CU end and R2 wander to verify as many far point earths as can  sensibly be reached and note the highest ... )

Mike.