As you probably know by now, the Northern Line is closed today after the Unions called for the trains to be withdrawn due to safety concerns.
The whole thing came to a head last night after a train's emergency brakes failed (despite the high-tech rope-based system used) and it ran through a red light...which sounds like a safety concern to us.
This was the fifth incident on the line and as a result four workers were sent home after they refused to drive trains. Both the RMT union and Aslef then said that they would support any members who refused to work on safety grounds.
Aslef has also said that it will ballot members over industrial action on Thursday if drivers are sent home without pay, while both unions are due to meet London Underground representatives later today.
For their part LU issued a statement which said "We are working on a solution to improve the maintenance of Northern line trains."
You can find TfL's travel advice page here, that has all the replacement bus service details.