I am in the USA and the ba.com home page is loading normally for me. I suppose it was a temporary glitch on their end. Is the site back up for you?

Many thanks. Sadly, the problem persists. So I don't think this is a temporary glitch on BA's part. i suspect it may have more to do with something on my laptop, given that I get the same error message when using the MS Edge browser as well as Mozilla

Having the same problem with two browsers rules out things like addons or cookies, and kudos for mentioning your AV software. A 403 error is a "forbidden" error. The site acknowledges your request but denies it. So it's something the browsers both have in common, anything from the AV software (or other security software) up to your router(s) and IP address. Do you recall the last time something in this chain changed?

I suggest isolating the issue by swapping out all each these things, one at a time.

Can you temporarily switch off all the AV software? Or at least the web component in Kaspersky...assuming that's how it works? Any difference? While British Airways doesn't offer easy support, I'm sure Kaspersky does. They may even have other ideas.

You might talk to your ISP to see if they have suggestions. Did they supply your networking hardware? Also inquire about changing your IP address.

If you press F12 in Firefox, you'll see the developer tools. Click the Network tab, then try loading the site again. While you would normally see an endless list of network requests, in this case there should be just one, Firefox's request and the 403 response. Click the single (?) line, and note the section that appears on the right, hopefully with "Request Headers" and "Response Headers". If none of the other suggestions gets you anywhere, would you upload screenshots of the single line (without the sidebar, in case any information gets cut off), and the full Request/Response section? If there's too much information in the latter, just copy and paste the text. You might also toggle the two "Raw" switches, so no data gets overlooked.

Does going directly to https://www.britishairways.com work ?

If you use a bookmark to access a specific page, instead navigate to this page starting with the main page or with the sign in page in case there is a problem with this bookmark.

You can try these steps in case of issues with webpages:

You can reload webpage(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Settings), click the padlock icon (Clear cookies and site data) for the domain in the selected tab.

"Remove the Cookies" for websites that cause problems:

• Settings -> Privacy & Security
  Cookies and Site Data: "Manage Data"

"Clear the Cache":

• Settings -> Privacy & Security
  Cookies and Site Data -> Clear Data -> [X] Cached Web Content -> Clear

• https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox
• https://support.mozilla.org/en-US/kb/how-clear-firefox-cache

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can check for issues with Enhanced Tracking Protection. Firefox shows a purple shield instead of a gray shield at the left end of the location/address bar in case Enhanced Tracking Protection is blocking content.

• click the shield icon for more detail and possibly disable the protection

You can check the Web Console for relevant-looking messages like blocked content.

• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop
• https://support.mozilla.org/en-US/kb/total-cookie-protection-and-website-breakage-faq
• https://support.mozilla.org/en-US/kb/trackers-and-scripts-firefox-blocks-enhanced-track