Bold statement
"We believe focusing on the City is right because no one else sells full coverage fiber directly to businesses in central London at a minimum of 10Gbit/sec,"
So the Vorboss site is.. rather light on details about how the service is actually provisioned. It makes some interesting claims like being an ISP offering 'full 10Gbps'. I'm guessing the SLA doesn't guarantee that, and it'd be fun to provision. From a quick poke, Vorboss is part of Fern Trading, who bought them and Giganet recently. But Nx10Gbps would need a decent chunk of transit, peering and some BFRs to deliver.
There's also plenty of competition from other suppliers, it being the City and all. Many of which have been digging up streets and overbuilding for a lot longer, so may have more buildings 'lit', or at least proximate. Most of them also offer 10-100Gbps services, so the USP seems to be the fixed price and no install. That's mostly a commercial thing, but the costs of 'last mile' connectivity around the City can get very high. As can the actual provisioning, ie how many optical nodes a 100Gbps have to transit. Maybe they're going to try for a mostly passive solution, but that'll have a big impact on SLA.