A UK creditor can usually claim Late Payment Interest and Compensation from a debtor outside the UK, provided one of the following applies:
The law of the contract is English either under normal rules or because the contract says so.
One of the parties is in the UK or the contract is to be performed in the UK, and there is a clause in the contract giving the English courts jurisdiction
If the law of the contract is under a country within the European Union then it may be possible to claim under that country's own implementation of the European Late Payment Directive 2000/35/EC.
What Can I Claim In Different Countries?
Broadly speaking, the EU Directive sets out the following minimum criteria on what you can claim:
Interest at 8% above the appropriate reference rate (usually either the official interest rate for that country or the ECB interest rate for countries inside the Eurozone)
Compensation of at least €40 (individual member states are allowed to specify higher levels of compensation)
Any reasonable costs of recovery above the statutory compensation (such as solicitors fees, legal costs, etc)
If you want to find out more the European Commission has a website dedicated to the Late Payment Directive.