Hello, 

10-12 months prior to enrolment 
• This is the time when you shift from the preparation mode to creating the application. Think hard about what makes you unique as an applicant and sketch out your strengths and self-assessment.
• Register yourself and start preparing for required standardized tests like GMAT,GRE, UKCAT,TOEFL or IELTS - depending on the course and university.

For more information plese go through the following link 

https://studyabroad.shiksha.com/student-guide-to-the-united-kingdom-uk-guidepage-16

Hope this helps..