If you are unable to pay your tax bill on time the best course of action is to let HMRC know and agree to set up a “Time to Pay” plan.
This can avoid hefty late payment penalties being applied to the balance of tax owed. You will need to keep to the repayment plan agreed.
HMRC could make you pay the remaining balance in full if there is a default on the plan. A repayment plan can be set up online or by calling HMRC.
See https://www.gov.uk/difficulties-paying-hmrc for further details including how to set up the plan and the conditions to meet in order to agree a time to pay arrangement.