Are you getting this message when trying to access the site or after you've logged into your account?

I don't have an account with them. I missed a parcel delivery this morning and wanted to arrange a redelivery. I have done this on several occasions in the past without problems.

Try this. https://support.mozilla.org/en-US/kb/remove-websites-address-bar-suggestions

"You don't have permission to access..." errors are characteristic of a firewall that protects the server against misuse and this firewall thinks something is suspicious about the HTTP request. If you use a proxy or VPN then try to use a direct connection. Select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

• Settings -> General -> Network: Connection -> Settings

You can try to clear the Cache and remove the Cookies for websites that cause problems via the padlock button or via "3-bar" Firefox menu button (Options/Preferences) to see if that fixes it.

• https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

I've seen cases where having enabled "Resist Fingerprinting" was causing this issue.

• https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting

If this all doesn't work then you can try "Forget About This Site" in the right-click context menu of an history item.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

I had tried clearing cookies via the padlock icon, that did not help. I tried removing cookies via the privacy & security > cookies and site data > manage data > remove selected. Neither of these made any difference. I closed Firefox browser and went and did other things. After opening Firefox again I tried the site again and was successful. The problem has gone for the time being, but no further forward in finding the cause.

Hi

It looks like Royal Mail had a few problems earlier today:

https://www.bbc.com/news/technology-64110269

Thanks to all for input, but it appears that Royal mail were the culprits after all.