Invoice with no Late Payment T&C

Hi,

I'm relatively new to freelancing and I have an invoice which is now 3 months overdue. I'm in contact with the client, and their accountant, and they are waiting for a chain payment form their client.
Unfortunately, my original invoice does not have late payment t&C. However they did make a payment of 30% deposit before my services started.

I am now confused how to legally approach the client. What are my options?
Can I send them a letter saying I will now be charging for Late Payment? Or shall I just inform them that I will be passing this straight to a collection agency?
Hope you can advise.

Thanks,
Ian

I'm pretty sure that the 1998 Act states that unless there are agreed terms and conditions to the contrary, the payment must be made within 30 days.

Thanks,

So, I am with in my rights to charge late payments with out stating it on the original invoice.

Then my next letter to the client would be:

THIS

Is this correct?

Thanks,
Ian

That's great.
Thank you for your time. I will sign up as a supporter. Its always good to to have a reference like this.

Thanks,
Ian