Ex driving instructor here so I have somewhat of a clue, Basically your no claims will only last 2 years at last check after that you lose anything you have regardless of how much you had.
You can say you have been using a company vehicle which of course you will have been doing but you'll need to provide evidence. Which usually means contacting someone at head office and getting a statement of some sort. I'm speaking generally here I have no idea if Openreach supply this or who you contact at OR I just know its likely to work that way based on experience and previous knowledge.
Not all insurers will care and if they do it will likely not generate the same kind of discount a no claims would.
To be perfectly honest though a no claims doesn't help much these days since they put their prices up each year its rare you save very much its just good for them to make it look like you did