Its probably only a cosmetic issue rather than an actual problem.
Your connection was likely going via Manchester anyway to get to the rest of the Internet. You can see a map of Zen's network here: http://www.zen.co.uk/about-us/our-network
(Click the core network button)
From that diagram you can see that all of Zen's external connectivity (Peering and Transit points) are in London or Manchester.
What really matters is end-to-end latency. I doubt that has actually changed significantly.