Traceroute looks a little odd with the double final hop.
Doing some manual ones, the 6ms jump inside the Zen network between London and Manchester is high, but if consistent no issue
Am seeing some packet loss via traceroute as sometimes pauses, but oddly when I try to ping the IP directly I get no response at all. Being able to traceroute but getting no ping responses to me suggests something configuration in the router.
Time to drop a different modem/router onto the line to rule out oddity in the Fritzbox
Reason being that at times there are distinct patterns to your ping, and even when connection looks idle the packet loss is not reflected by an increase in average latency usually (this changed at 10 pm last night maybe using connection?)