Oil Tank Regulations

I have a 1200 litre steel tank (6 ft x 4ft x2ft), for domestic heating oil, inside a stone outbuilding (35 ft x 16 ft) and supplying my house only. The connecting pipe is above ground and everthing is in almost "as new" condition - due to many layers of "red lead" and hammerite applied before and immediately after it was installed. The conventional boiler is actually 55kW and should have had a bigger tank (IIUC), but the previous tank was that size and only needed filling once a year.
Now, I understand that the rules have changed regarding tanks?
I am planning for the tank to go in a year or so anyway - as I want to turn the outbuilding into a garage. However, I am not sure whether it is "legal" to get it filled, this year. As I understand it, any new tank has to have secondary containment, which this one doesn't.
Any thoughts, greatly appreciated.

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