You will receive your Certificate of completion which is posted to your address. This confirms that you have had guided English language training at a certain level and you have successfully completed a number of tutor-marked assessments. Usually, this is a sufficient proof of your language competency and many employers and institutions accept our certificates.
You may require a formal ESOL qualification in which case, you will need to book your face to face exam. Read more here. This is optional.
Also, you may be interested in SELT (Secure English Language Test) if you want to apply for citizenship or visa for example. This is booked through Trinity exam centres.
If you are applying to study, work or live in the UK and require a formal proof of English language competence, you should contact the institution you are applying to directly to find out their requirements.