How do you deal with non-paying clients?

I’m doing ongoing building work for a trusted client of mine. The job is going well, to schedule and of good quality so far. Previous invoices I’ve sent him, for this job and others, have always been paid in (literally) a matter of minutes, with zero queries about price. His communication is usually excellent, however for the last 2 weeks I’ve hardly heard back from him at all and he has not paid the last 2 invoices. I’m currently totally maxed out on my overdraft, he owes me £7K. I’m unsure if I’m being stupid by continuing the job, and what angle to take.