From the Thameslink website:

That's an alternative is it? Wait another 15 minutes (if you are lucky). As for Penge West and Anerley passengers changing at New Cross Gate, they obviously mean Norwood Junction but are too inept to know the difference.

In the past I have used Norwood Junction to turn around and come back faster than waiting for the next train, this is preferable to waiting 30 minutes between trains and at least you get out of London Bridge.

If they were serious about providing alternative routes then they would say that tickets to West Croydon will be valid on Jubilee and Overground. But they would prefer passengers to hang around at London Bridge for double crowded trains rather than take alternative routes (which I realise would add to pressure on the short Overground trains - but I don't see stuffing twice as many people on London Bridge trains as much better).

I can't believe that after the problems in August and a chance to adjust the timetables (including cancelling a small number of services), Southern have yet again failed to run trains in and out of London Bridge according to the timetable. They really should have planned better for this situation.

It will be interesting to see if services improve when South Eastern services stop calling at London Bridge. As davidwhiting says, if this is the problem then why didn't they make the change on the 4th January, straight after the complete closure of London Bridge?