Hi, are you starting here: https://www.gov.uk/check-vehicle-tax

Then there is a Start Now button that leads here: https://vehicleenquiry.service.gov.uk/

Of course, I don't have a real number to search, so I can't really investigate further, but is it working normally up to that point?

What is the address of the page that has the error message? Please insert a space before the .gov.uk part so that your reply isn't held in the link spam queue.

(And just FYI, this site doesn't accept email replies, so please return to this thread at https://support.mozilla.org/questions/1445576. Thank you.)

Does it still happen in Troubleshoot Mode?

https://vehicleenquiry.service. gov.uk/cookie-policy?locale=en&referrer=%2Fcookie-policy%3Flocale%3Den

Above is the page that defaults. I have also tried by turning the tracking blocker off as well with the same result

Oh, duh, I just rejected analytics cookies and moved on.

If I start from https://vehicleenquiry.service.gov.uk/ and click View Cookies, then that page loads fine. However, I am puzzled why your url has this on it:

&referrer=%2Fcookie-policy%3Flocale%3Den

That isn't added to mine. If you remove that part, does it work?

Have you tried clearing site cookies and disabling your extensions?

Try changing DNS over HTTPS (DoH) to "Off" or "Max Protection" and in Connection Settings change "Use system proxy settings" to "No proxy".