Online system logins are prone to identity and transaction theft by trojans. OTP and other 2 factor authentication systems cannot stop them.
Xchq lets a user login to his online services sites like banking, trading, tax, medical insurance, online payment etc SECURELY without fear of his credentials being stolen by phishing or trojans. Further, transactions that a user conducts e.g. money transfer, credit card payment, stock sale etc are also protected from any kind of online theft/ hijack.