Access to my hosting server at 123-reg

Try with your computer using a Public DNS like Google DNS 8.8.8.8 & 8.8.4.4
This is to be quite sure the VM Web Safe filters are out of the frame (as opposed to just look to be turned off).  

Thanks for taking time to reply.

Tried Google DNS / Public DNS. Doesn't work. Guess, somehow need to get hold of someone relevant in Virgin Media. Any chance, you know the right contact point, perhaps from your past experience, to get certain URL/IP removed from the filters ? 

For false positives from Web Safe one needs to email the details to : websafefeedback@virginmedia.co.uk

However when using the Google DNS you totally bypass the VM Web Safe (Virus Safe and Childs Safe) filters.

Hub 5 in Router mode did have some reports that the DNS lookups timed out for some sites,
this could be tested with an NSLOOKUP command & observe if the expected IP is returned or the lookup fails. 

I contacted VM through their chat support and I was told following -

'I checked for this information and I see that the URL is listed as blocked from UK government so as this is blocked by UK government it is not possible to view access through virgin media broadband connection.'

'I am really sorry to inform that, there are certain IP addresses and links which are restricted by UK government for all the broadband service providers due to the risk and threat they contain, as you said you are able to access it from mobile data, I request you to use mobile date for such links or IP addresses.'

Really, this is a GoDaddy server, which I can use from mobile which is O2 - which is VM.

 😭

I smell a hundred and one dalmatians rats in that chat support explanation.

Both VM's home & business internet service and O2's  GSM mobile data service
are required to fully comply with UK Government IP blocking orders.

Thanks for your support. I have written to VIRGIN to see if it is blocked/black listed.

Meanwhile I tried the nslookup and there is something that says 'uk-blockpage' which makes me think this could be VIRGIN's validation issue. I will post the resolution later if they come back with anything. Apologies if I repeat some things, as I am not very techie.  

The web hosting commented that - 'This means that there may be a VPN/Firewall blocking the connection on that network' which was mentioned by yourself as well.

The host named  uk-blockpage...   is the DNS that is failing to perform the name lookup of your host.
Try specifying a different DNS for your nslookup such as the VM DNS 194.168.4.100 (results below) or Google Public DNS 8.8.8.8 (also resolves your host name to two IPs )

C:\Users\Philip>nslookup host.secureserver.net
Server: cache1.service.virginmedia.net
Address: 194.168.4.100

Non-authoritative answer:
Name: wingcorepx-hcx-spa-shell-prod.wingcorepx-prod.prod.onkatana.net
Addresses: 44.237.12.134
44.226.211.99
Aliases: host.secureserver.net

Hope this is what you meant.

That is exactly what I hoped you would try.  
Sadly it looks like your choice of DNS is being redirected.

The link below performs the NSLOOKUP off the VM platform & it works returning the two IPs ...
https://www.nslookup.io/domains/host.secureserver.net/dns-records/#google   


Using the link ... 'https://host.secureserver.net/webhosting/cpanel/account/.......'    I get to :

Are you using antivirus software or malware protection that relates to or is routing your network traffic through  : https://securingsam.com/  ?