London’s mobile networks are too slow for AI voice assistants
Key Points
- All 19 London areas tested missed Ofcom’s 50 ms latency target
- London averaged 72.71 ms across the areas tested
- AI voice assistants need 30 ms or less to feel natural
- Eversholt Street recorded the worst latency at 96 ms
- Most London 5G still runs on older 4G core equipment
A new test shows that London’s mobile network service is largely too slow for AI voice assistance, putting the city on the back foot in the race for AI adoption.
Every one of 19 London areas tested missed Ofcom’s 50 ms latency target, with an average of 72.71 ms, according to the GLA and Ookla.
The Greater London Authority (GLA) and Ookla published the figures in their report A New Lens on the Connected Capital, based on about 10,900 outdoor tests across all four major UK mobile networks.
Latency measures the time data takes to travel from a phone to the network and back. The report found that AI voice assistants such as those built on OpenAI’s Realtime API or Google’s Gemini Live need latency of 30 ms or less to feel natural.
Latency of 70 ms or more breaks the sense of conversation, according to the report. London’s average of 72.71 ms sits above that level.
The report explained that natural conversation leaves a response window of 200 to 500 ms. The AI model itself takes 200 to 300 ms to respond, which leaves the network only a small share of that time.
Video calls also suffer at London’s latency levels. Microsoft Teams, Zoom and Google Meet all target one-way latency below 50 ms for a high-quality experience.
Only Old Street at 51 ms and Chapel Market at 55 ms came close to the 50 ms target. The worst-performing areas recorded the following latency:
- Eversholt Street / Somers Town – 96 ms
- Brick Lane – 83 ms
- Kings Cross Boulevard – 80 ms
- Leadenhall Market – 80 ms
Latency also varied by network. The most responsive operator averaged 66.99 ms across London, while the slowest averaged 83.88 ms.
The report linked London’s high latency to dense urban conditions, limited capacity on the links between masts and the wider network, radio configuration and core-network routing. It did not attribute the problem to any single factor.
Most consumer 5G in London still runs on older 4G core equipment, according to the report. That setup boosts speeds but does not deliver the very low latency of standalone 5G.
