The UK's Registered Traveller program requires frequent visits to qualify for an initial application. Once qualified, are continued frequent visits to the UK required to retain Registered Traveller status?
Registered Traveller status is valid for 12 months from the day you submit your application:
The immigration officer will check that you meet the criteria and tell you if you can become a member. Your 12 month membership will start on the day you submitted your application.
After that, you need to renew your application on a per-year basis by paying additional fees. At this stage, I assume you need to prove / meet the same criteria as for normal applications which is "at least 4 visits to the UK in the past 24 months".