The payment due in July is like an “instalment” for next year’s tax. HMRC will use your circumstances last year as a basis for setting these.
As you have missed the deadline, HM Revenue & Customs (HMRC) may now charge you interest on the amount due until the date you eventually pay it.
If you are struggling to pay, you could phone HMRC and ask if they could arrange a payment plan for the outstanding balance. They tend to prefer the tax not to be overdue already though, so this may not be too successful.
Alternatively, you could prepare and submit your tax return. This will then trigger the calculation of your actual tax bill, which will then be compared with these instalments (called Payments on Account).
Please feel free to contact your local TaxAssist Accountant if you would like to discuss your Payments on Account further or would like some help completing your tax return.