Dangerous goods advice- UK regs and ADR

OK, had a chance to look round the steel IBC’s in the yard today.

I’m not sure where I got the 1100l from there’s nothing on them except for a big label with the companies name and details etc. and 110% bunded fuel flask.

There is a little embossed serial number plate however and it gives the unladen weight as 500kg Laden at 1500Kg, assuming diesel weighs 1Kg per litre this would make it a 1000l IBC would it not?

The next task is to present my findings to the boss, might take a while as one of them has just gone away. I’m not too worried as it’s not something that has occured, just that it might.