One of two things: A block on the Virgin Media DNS (domain name server, the internet's address book). Sometimes this blocking is unintentional, sometimes there's a specific reason (eg illegal content, pirated software sites, malicious web sites etc). Or it may be geo-blocking by the server, who don't wish to allow access to VM customers (either to control intellectual property rights, or to avoid the hassle of EU data protection law).
When you use Opera's VPN then you're using their choice of DNS, but also the web site sees your connection as coming from the VPN end-point, so you would appear (for example) to be a US internet user. This invariably breaks ISP adult content filtering, and for most free VPN's you will be anonymous to the sites you visit, but you won't have high levels of privacy because if you're not paying cash, then you are the product, and they will probably record your activity and find a way to make money from it.
Regarding the DNS, Windows usually defaults to the ISP's DNS, Google hardware and software products usually default to the Google DNS, Amazon default to the Amazon DNS, and so on. Everybody wants you to use their DNS so that they can sell your data (including Virgin Media). Probably the best option is to instruct your devices to use the Cloudflare DNS, as that's fast and (within limits) secure so long as the user isn't connecting to illegal content, but you need to know the consequences of having a mostly unfiltered DNS. A search on Cloudflare DNS will explain what to do if you wish.
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It works for me although I do have my hub in modem mode and I use 220.127.116.11. Here's my trace route.
Tracing route to bsug.net [18.104.22.168]
over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms 192.168.1.1
2 * * * Request timed out.
3 12 ms 10 ms 11 ms haye-core-2a-xe-233-0.network.virginmedia.net [22.214.171.124]
4 * * * Request timed out.
5 * * * Request timed out.
6 21 ms 20 ms 18 ms tele-ic-6-ae2-0.network.virginmedia.net [126.96.36.199]
7 18 ms 19 ms 17 ms 242-14-250-212.static.virginm.net [188.8.131.52]
8 22 ms 18 ms 19 ms xe-3-3-1-0.core1.lon2.uk.m247.com [184.108.40.206]
9 35 ms 33 ms 23 ms te-12-8-0.core-dc2.man4.uk.m247.com [220.127.116.11]
10 24 ms 25 ms 24 ms eth-13-0.core-dc2-agg1.man4.uk.m247.com [18.104.22.168]
11 25 ms 25 ms 26 ms te-1-49-0.xs2a.man4.uk.m247.com [22.214.171.124]
12 25 ms 27 ms 26 ms phantom.ukwebsolutionsdirect.com [126.96.36.199]