The walkways have historically been staff only (officially) but have recently been converted for passenger use. You can now take the lifts that go down to the TTS platform in A one level further to the walkway level. The same applies in B, and in C you can just walk through the doors at the end of the platforms.

There are separate walkways for arrivals and departures, and they now have travelators and signage, with improved lighting etc.

It is only quicker to walk if you have just missed a train and/or the platforms are very crowded.