Coronavirus - grant funding could save business but have not been paying business rates

[busfull]

Don't think my husband's small business will survive this. The grant funding available is only for those SMEs that are eligible for small business rate relief. This could have been a life-saver BUT I have just found out my husband hasn't been paying business rates. This is not as awful as it sounds initially as the business started in an ex pig shed on a farm. It was assessed for business rates and he was told it was exempt due to being an agricultural building (it wasn't very big either so pretty sure it would have been under the 12K rateable value threshold). Problem is the business relocated to a neighbouring farm (this time a cow shed) 10 years ago and I just found out that my husband did not report the change in premises (assuming it would be similarly exempt - it was pretty much a like for like property). The business has now grown - still in a cow shed but with a yard and an additional storage barn alongside. The rent is sufficiently high now that my husband won't be able to pay it and will have to lay off staff (4 employees now) as a result of coronavirus disruption. Don't know what to do now. Should we stay below the radar and try to mothball the business and start up afresh or hold up our hands and get the property assessed now (and face potentially crippling backdated rates). Any advice very welcome. This was a genuine mistake originally but I suspect as the business grew my husband knew he should have had the premises assessed :-(