It is preferable to have completed at least the Day Skipper course and apply then an ICC (International Certificate of Competence) to be able to charter a boat in local water and foreign countries. Note that some countries require specific certification. Like in Malta, if you are a Maltese resident, you also need a Transport Malta Nautical License in order to crew and drive a boat in Maltese water.
You are also recommended to take the RYA Marine Radio VHF course. The VHF course will be useful if you want to do chartering in the future, because you are required to hold a VHF certificate for that purpose.
The ICC (or to give it its full title International Certificate for Operators of Pleasure Craft) is a certificate which is intended to provide evidence of competence when requested by officials in foreign countries. It was historically known as the International Certificate of Competence.
Learn more about the ICC, its history, what it does and doesn't do, and where it might be accepted, check here:
https://www.rya.org.uk/knowledge/abroad/icc/evidence-of-competence-abroad For Competent Crew: RYA Competent Crew Skills:
https://www.rya.org.uk/shop/p/rya-competent-crew-skills