There could be direct rail links between London and Germany from the early 2030s, after Eurostar signed an agreement with Deutsche Bahn (DB).

If the service launches, it would likely see journey times of four to five hours between London and Frankfurt, with possible stops at Cologne and Brussels. Although that would be slower than flying, it would be comparable when you factor in that the railways would drop people off right in the centre of the cities, unlike airports, which also have long waiting times before departure. And of course, there are the environmental benefits of trains over planes.
Although the new announcement is only a Memorandum of Understanding (MoU), which basically says they will work together and doesn’t guarantee a service will happen, in principle, it means the two are trying to get it up and running.
It would also be Deutsche Bahn’s second attempt to run services to London, following cancelled plans in 2010.
Eurostar says the service would use its new double-decker Celestia fleet, targeted for the early 2030s, provided that the necessary technical, operational, and legal conditions are met.
There might be a problem there, as it may be challenging to run the Celestia fleet through the Channel Tunnel in their current configuration unless regulatory requirements for tunnel evacuations change.
In fact, as Jon Worth points out, Deutsche Bahn had planned to use similar trains a decade ago before abandoning the attempt. However, at the time, they did say they had a solution that would allow their trains to run through the tunnel.
In addition, due to the complexity of international rail travel, the government ministries of both countries have established a task force to jointly address the political challenges to a direct link between Germany and London, particularly regarding entry formalities, the necessary infrastructure, and intergovernmental agreements.