Cookies
Nothing is loaded before you say yes, and rejecting takes exactly the same number of clicks as accepting.
If you do nothing
No analytics runs and no analytics cookies are set. The script is not loaded at all, so nothing is sent anywhere. The site works exactly the same either way.
If you accept
Google Analytics loads and sets its own cookies, which let it recognise a returning visitor and work out roughly how many people read a page. It records which pages you visited, roughly where in the world you are, and whether you clicked a button or started the enquiry form. IP addresses are anonymised.
I use it for one thing: knowing which pages are worth keeping.
The one thing stored either way
Whichever you choose, your answer is saved in your own browser’s local storage so you are not asked on every page. That is not a cookie, it never leaves your device, and clearing your browser data removes it.
Change your mind
Rejecting stops anything further being sent. Cookies Google has already set are removed by clearing site data in your browser.
Everything else
What the enquiry form collects and how long it is kept is on the privacy page.