Netflix has begun its crackdown on the millions of UK subscribers who share their passwords with friends and family who live outside of their household. The streaming company has sent a letter to almost four million British subscribers that it has identified as giving friends and family members outside their home free access. About a quarter of Netflix’s 15 million UK subscribers are estimated to share their password, according to research firm Digital-i. Despite years of overlooking password sharing, in the letter Netflix has reminded password sharers that their account “is for you and the people you live with”. “A Netflix account is for use by one household,” the company said in a blogpost on Tuesday. The company has estimated that people in about 100m homes that pay for its service globally share their passwords with friends and family. It has set up a “paid sharing” offering where extra users can be added for £4.99 a month. Netflix has advised telecoms companies including Sky, Virgin Media and BT to brace for a potential backlash from customers who view its films and TV shows through their services. The “extra member” feature is currently not available to Netflix users who sign up through third parties. Netflix is getting tougher with password sharing as one of a number of moves to increase profitability after new subscriber growth rates slowed down. In the email, the company said: “Your Netflix account is for you and the people you live with – your household. “You can easily watch Netflix on the go and when you travel – either on your personal devices or a TV at a hotel or holiday home.” It said that users could review which devices are signed in to their account and “sign out of devices that shouldn’t have access and consider changing your password”. The company said users could transfer a profile on their account to a new account, or add an extra member. The world’s biggest streaming service had already begun to crack down on password sharing in regions including Latin America, New Zealand, Spain, Portugal and Canada. Netflix has also responded to the cost of living crisis by launching a new pricing tier, at £4.99 a month in the UK, which includes advertising for the first time.