Update on X/Twitter from Network Rail
. It explains the source of the failure.
UPDATE: Work to bring the signalling back online between Eastleigh and Brockenhurst continues. We hope to get the system restored tonight, but the knock-on impact means @SW_Help is advising against non-essential travel on the route tomorrow
After upgrades to the signalling control systems at Eastleigh Area Signalling Centre overnight, we experienced a power surge which meant that damaged components needed replaced, the signalling control system rebooted and all the specialist signalling software reinstalled.
That work has taken longer than expected and we haven't been able to restore signalling as quickly as wanted.
Adding
Signalling restored just before 23.00 hrs