Is an all-pass filter a linear phase shift filter?
I think what you are looking for relates to the term group delay. Here's an example of 1st order to higher order all-pass-filters: -



Group delay is: -


  In signal processing, group delay is the time delay of the amplitude
  envelopes of the various sinusoidal components of a signal through a
  device under test, and is a function of frequency for each component.


Back to your question...


  does a standard 1st order all pass filter provide a linear phase
  shift? if not, what circuit provides a linear phase shift similary to
  a Bessel filter, whilst providing linear amplitude response?


With reference to the picture above, you should be able to see that a 1st order circuit doesn't provide linear phase shift however, if you increase the number of stages then you get an improvement.

The picture was taken from Chapter 16 Active Filter Design Techniques by Texas Instruments