If you see a CLI of 0800 xxx xxxx, it is always a fake CLI, even if it is coming from the owner of that number, because an 0800 number redirects to a geographic number, or possibly a group of geographic numbers.
The caller may want you to call back on the 0800 number so they can distribute the calls around their call centres, and anyway it is free to call that number whereas the geographic number might not be, depending on your phone contract. My contract gives me unlimited minutes, so it would be free anyway, but only for calls of up to an hour in duration. Other people might have to pay for them, so 0800 nos are never a bad thing. And if the geographic number is in India, it would almost never be free from the UK.
How do you allow that without allowing fraudsters to fake CLI? I suppose it would be possible to have a system where the owner of the number can specify permitted geographical numbers to call from.
Biting the hand that feeds IT
