The message below is what I received from Google. I have had to lower my security setting!
Access for less secure apps has been turned on
You received this message because NTLWOrLD is listed as the recovery email for GMail If gmail is not your Google Account, click here to disconnect from that account and stop receiving emails.
You recently changed your security settings so that your Google Account GMAIL is no longer protected by modern security standards. Please be aware that it is now easier for an attacker to break into your account. You can make your account safer again by undoing this change here, then switching to apps made by Google such as Gmail to access your account. Don't recognize this activity? Review your recently used devices now.
I think what Google is saying is that NTLWORLD is not a secure app or out of date. I use my ntlworld email address as the security email address for Google. What I want to know is why is Virgin media running an unsecure email service or why is it not up-to-date?
Google like everyone to use the security choices they made. Sometime this is a good thing. Other times this goes against internet standards. If you don't use Google's security choices, they'll send warnings to you to try and get you to do so.
As far as I know using an ntlworld.com address as your recovery email shouldn't give the prompt above.
If you don't check your Gmail account using another webmail service (such as Virgin Media Mail) or email program, you should check your device activity here https://myaccount.google.com/device-activity to make sure you recognise all the devices listed.
********************************** I work for Virgin Media - but all opinions posted here are my own
You may well be right but (IMHO) the recovery email address (account) should be as secure as possible and in that respect it is not, for example, allowing a password to contain all printable ASCII characters, including space character.