Tristán White wrote:

It's a bit like the Wembley Park problem, knowing which one to take.

The current situation at Wembley not only creates a passenger information
problem, it also makes a bit of a mockery of the cross-platform interchange
with the Jubbly. The correct solution is to have extra crossovers west of
the station so that fast trains to and from Harrow can use the platforms on
the slow lines at Wembley. There is no need for off-peak Met trains to
overtake each other between west of Wembley and Central London, so there's
no reason to use the fast lines at Wembley outside the peak. The platforms
on the fast lines at Wembley could then be shut completely except during
Wembley events, where the extended dwell time might necessitate using all of
the platforms.