That's part of the Virgin network...
Tracing route to
www.vmspeed.com [80.0.239.6] over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms Tomato.HomeRouter [192.168.0.1]
2 10 ms 9 ms 10 ms cpc5-nrte25-2-0-w.8-4.cable.virginmedia.com [86.21.48.1]
3 11 ms 19 ms 12 ms nrth-core-b-ae2-2562.network.virginmedia.net [213.106.254.97]
4 8 ms 11 ms 12 ms nrth-bb-1b-ae8-0.network.virginmedia.net [213.105.159.209]
5 47 ms 19 ms 9 ms popl-bb-1a-as3-0.network.virginmedia.net [213.105.172.14]
6 13 ms 20 ms 17 ms asfd-core-1a-ge-00-0.network.virginmedia.net [212.43.163.29]
7 24 ms 19 ms 15 ms asfd-tam-1-ge01.network.virginmedia.net [80.3.97.22]
8 21 ms 24 ms 19 ms host80-0-239-6.no-dns-yet.ntli.net [80.0.239.6]
Trace complete.
Other speedtests (along with the rest of the internet) rely on VM's links to the internet and if they are congested you'll see poor speeds. Of course it could also be that every speedtest site you tried is congested and VM are perfect but I somehow doubt that.