Upvote:2
On the face of it, staying longer than originally planned as a visitor but leaving within the 6 monthsβ visa validity period does not breach any Immigration Rules.
The UK makes a distinction between information that is false but where the ECO is not satisfied there was an intention to deceive by the applicant and cases where the ECO is satisfied there was deception by the applicant.
Visa decisions are made on the basis of the information provided in the application at the time the application is made. If, for example, an applicant stated they planned to stay 2 weeks and showed intention to leave by proving they had a job to return to, and then on receipt of their visa resigned their job to be able to stay (much) longer, such a material change in circumstances and non-disclosure of it at the time of seeking entry to the UK might be construed as false representation or deception. Note: IANAL.