The guidance states very explicitly that no child can go to lessons / be in school normally until the first test is taken and proves to be negative
As guidance it cannot explicitly state anything, and indeed as the extracts below show the guidance doe not - obviously - state this.
www.gov.uk/government/publications/guidance-for-full-opening-special-schools-and-other-specialist-settings/mass-asymptomatic-testing-in-specialist-settings
Importance of testing secondary age pupils and students
Settings should not make it a requirement to have been tested in order to attend their setting. Testing is voluntary and no child or young person will be tested unless informed consent has been given by the appropriate person and the child and young person is willing to be tested. If assisted swabbing is required, the willingness and feasibility to swab should be reviewed and risk-assessed every time before swabbing. Further guidance is available in the informed consent to testing section.
However, we strongly encourage all children and young people who are receiving face-to-face education to have the test, wherever it is possible to do so, to help identify asymptomatic positive cases and support appropriate self-isolation to break the chain of transmission.
Testing is similarly voluntary for members of staff and they are encouraged to participate.
Informed consent to testing
Testing is voluntary, but those who are eligible for tests are strongly encouraged to participate to reduce the risk of transmission within schools and colleges....... Settings should not make it a requirement to have been tested in order to attend.