AndreaC wrote:
I'm about to start a new job and this will involve travelling from
Hounslow to Warren Street.

If I use the train it's a simple case of going to Waterloo and then up
on the Northern line, but I'll also have the option of using the tube.
The most obvious route there seems to be Piccadilly line to Green Park,
change to the Victoria line there and go on to Warren Street.

However, I seem to recall that once, a long time ago, in the vague
mists of time I tried to change or possibly even exit at Green Park and
it was a flipping horrible station to navigate.

The alternative as I see it is to stay with the Piccadilly line to
Leicester Sq and then change to the Northern line there.

Any suggestions or advice from those of you who know these things
better than me? Any idea of journey times?

If your station is Warren Street then you might find Euston Square,
Great Portland Street or Regents Park just as convenient to use.

If there is a mainline train to Paddington then you can take that and
continue the journey from there. From the Piccadilly Line, you can
change easily at Piccadilly Circus for Bakerloo Line or change at
Gloucester Road for the circle although I don't recommend that.
Hammersmith for Hammersmith & City Line requires an interchange at
street level but if you're prepared to do that it may be your best
option.