For getting Citizenship ,you may need to show you or someone here in the UK can financially provide for you, have a job, or job offer, but the applications are not specifically looking at debts or money owed.
If your debt or the money you owe stems from a crime, such as fraud, money laundering, a court fine, or has a CCJ filed against you and has been through the courts, this can be another matter.
Criminal offences are reasons where a Visa and/or Citizenship may be denied.
So in addressing the questions regarding getting a Visa and extending it and having debts, in the majority of instances it is not going to be an issue
However it can be problem in getting Citizenship There is the requirement of the “good character ” for obtaining Citizenship here in the UK.
One of the requirements outlined in this part of the naturalisation process is of “financial soundness“.
There is a section that relates to and addresses debt, Section 6.2 states:
“The decision maker will not normally refuse an application simply because the person is in debt, especially if loan repayments have been made as agreed or if acceptable efforts are being made to pay off accumulated debts.