Thanks guys for the advice.

It worked a treat!

If you need to change from the Pic to the Vic line at Green Park, goto the
last car on the Pic line. The exit to the ticket hall is a min on the
esculator. And then another min going down.
Timed the interchange on my watch. 1 min 38 secs ( but I do walk really
fast!)

I think this is easier to get to Brixton from Alperton, as there is only 1
interchange. Compared with 2 using the D&C lines at South ken/ earls court.