In England it is ok provided it meets separation distances from controlled water sources like drains. 10 meters if I remember correctly.
Your oftec engineer will be able to advise on siting.
Since building regulations required it to be signed off by one.
You need to complete an OFTEC TI133-D risk assessment on the tank
as lon as there is no "controlled water" or loose fitting manhole covers within defined limits a single skin tank can be fitted, HOWEVER the advice I give clients is to fit a Bunded tank, to be sure that you are "future proof"
i.e. a few years ago, the powers that be decreed that all NON DOMESTIC oil storage tanks had vto be bunded, and the regulations were made "retrospective" meaning that all existing and previously legal tanks had to be brought up to the new standard (ouch!!)
Having re-read the OP's post I would further adivse that the OP should hold Qualification OFT 600A and therefore not need to be asking the question in the first place!!!
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