You may need a Construction Skills Certification Scheme (CSCS) card to work on a construction site. Although some of these options will list qualification requirements many employers are more interested in people who have a depth of experience in the construction industry.
You should explore the options to find out which is the right one for you. If you already have relevant experience, you could apply for a role directly. You can gain the qualifications you need by doing a university course or an apprenticeship.
There are several routes to becoming a clerk of works.