What I've done to avoid being put in this situation is put in intentionally punitive late payment terms (16% + base rate AER calculated monthly), and then hold

What I've done to avoid being put in this situation is put in intentionally punitive late payment terms (16% + base rate AER calculated monthly), and then hold customers to it if they start to play this game. This is double the statutory rate and if they're being really arsie I start adding on "reasonable cost" charges every time I have to chase an invoice. This works because every month (or even more freqently) they get a credit note for the old invoice and a new invoice with the interest and chasing fee added. This costs money not just in the added interest etc., but also in time. The way I figure it, the payment terms on my invoices are 30 days. The "real" payment terms (before I start doing the above) are 60 days. If you haven't paid by then, you're either incompetent, insolvent, or in danger of becoming so.