You can do a couple of traces from probes on the Hey/F&W network at
https://bgp.he.net/AS207645#_traceroute but they'll also be via Spain.
As jcre said, it looks like traffic Hey don't peer with in London they rely on AS49600/NEAR IP a Spanish company who interconnect with thier upstreams such as Cogent and GTT in Spain.
Then Adept don't publically peer very much, upstream with Cogent/GTT so the only option is to go via via Spain (or private peering)
There is probably not much that can be done, Hey/F&W could interconnect with their upstreams in the UK but they've gone through the trouble of doing it via Spain so it seems this is how they want it setup.
The other option is for Hey & Adept to setup private peering, which again seems unlikely given the amount of traffic likely to pass between them.
It's a really difficult 'problem' to get ISPs to fix, most would regard 50ms latency good enough and make no guarantees on latency, hence I think you'd have more luck getting Adept to try to find a solution.