We don't deal with council work, because 1) they want everything done every six months, and 2) they're not the promptest of payers - if you know what I mean. Contact the Head and ask what their payment procedures are. If they pay their own invoices on time - fair enough. If your invoices are passed on to the local council - just walk away, these guys take 6 months to pay.
However, if you want to factor this in - tell them your (increased) price includes a late payment surcharge and you'll give them a discount if they pay on time.
But I didn't say that - right?