Initially, you will need to send reminders yourself. Once it becomes apparent that further action is going to be necessary, then the two principal options are either to serve a Statutory Demand for payment or to issue a Claim for a Judgment in the County Court. Before a court claim is issued, it is necessary to send a formal letter of claim and instructing a solicitor to send such a letter is often sufficient warning for the Debtor to pay the outstanding sums.
Option 1: Statutory Demand
This is a formal demand, which must be made in a form compliant with the relevant insolvency rules, which gives the debt 21 days to be paid. If the debtor does not pay, then the creditor can apply to the court to make an individual debtor bankrupt or to wind up a company in the case of a company debtor.
Option 2: Claim via the County Court
This is a claim for the court to issue a Judgment confirming the debt is owed. It can be used where the debt is disputed, albeit the creditor will have to prove their claim to get judgment.