If you have all of the details of the contract available to you prior to agreeing to take out the policy then the cancellation period lasts for 14 days, with the day after you enter into the contract being 'Day 1' of that period.
[Section 10(2), Financial Services (Distance Marketing) Regulations 2004]
Where the insurer provides you with full written details of the contract
after you've entered into it you also have 14 days in which to cancel but 'Day 1' of that period is then the day after you receive those details.
[Section 10(3) of the Act]
So the insurance policy document you refer to is correct.
https://www.legislation.gov.uk/uksi/2004/2095/made