Today we received an alert that our site is not reachable from London location:
In that time we checked availability from London using a 3d party VPN and our site worked fine.
Please check and clarify, why your monitoring alerted?
This is to clarify that we didn't have any problem from our London location during the mentioned time period.
We received 404 status code from London location from your hosting provider after 2 redirects. It looks like a momentary issue in your end because the rechecks from other locations were fine which was performed immediately after London check. You would have received the headers information for that failure check in your alert mail itself.
In Site24x7 Webclient you can view the header information in the RCA in Outage tab of the Monitor details page.