Business Rates

[Exigeowner]

I have been given the opportunity to move into a Farm building where the owner is running another business from so I guess pays full business rates,

How does me moving into the building change things, do I just keep quiet or do I need to declare it somewhere ?

Of course I do not intend to break any laws but how much of an offence is it to say nothing, I assume its not like not paying VAT or Tax which as I understand is highly illegal/