There is no such rule for the UK. Immigration Rule V4.2 states “The applicant must satisfy the decision maker that they are a genuine visitor. This means that the applicant:
(a) will leave the UK at the end of their visit; and
(b) will not live in the UK for extended periods through frequent or successive visits, or make the UK their main home
There is an explicit statement on frequent/successive visits in the Home Office Visit guidance https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/793361/Visit-guidance-v8.0ext.pdf#page17 that states “There is no specified maximum period which an individual can spend in the UK in any period such as ‘6 months in 12 months’. However, if it is clear from an individual’s travel history that they are making the UK their home you should refuse their application.”
Each time you visit the UK in theory you are allowed to stay up to 6 months, starting from the date of entry stamped in your passport. If the Immigration Officer doesn’t feel this length of time is justified because your pattern of visits isn’t that of a genuine visitor, he/she can curtail the usual 6 months or even deny you entry.
As a rule of thumb, you should spend at least as long outside the UK as in it after every visit. The basis of your original application may also be a guide, for example if you said you expected to visit 3-4 times a year for two weeks to check on your sister during her studies. It might also be wise to have with you evidence of your ability to support yourself while in the UK and of your ties to home, eg job, plus of course a return ticket, to show to Immigration if asked.
As an aside, you should also bear in mind potential tax implications if you spend more than 183 days in the UK in a given tax year https://www.expertsforexpats.com/expat-tax/statutory-residence-test/