This sounds to me like a case of poor positioning: Your say "He is very
grumpy in between feeds -
dozes, then wakes and appears to be in pain - arches, screams, eventually
settles, dozes etc etc." As you mention, this sounds like colic - almost
completely curable in breastfed babies and down to positioning.  If the
baby is taking too much fore milk, the milk sugar will react in the baby's
gut to produce gas which will be extremely painful and hard to dislodge.
Some things to check are that baby is brought to mother, i.e. raised on
pillow; the nose is in line with the nipple which should point up and back
into baby's mouth; the chin is well tucked into breast and bottom lip is
curled back against the chin.

Funnily enough, these babies often have a good weight gain and of course,
their wet nappies are fine.  They sometimes produce a light green colour in
their stool which confirms the presence of too much milk sugar in the
system.

The other thing you mention is that the baby feels worse in the evening: 
this would probably coincide with the reduction in activity of the
breastfeeding hormones at this time of day.  There is not much one can do
about this except feed more at that time, it is not something that lasts
forever.

I often find that when the positioning is adjusted to ensure that all the
hind milk is being emptied from the breast, the baby will not react so
sensitively to this also.

Hope this helps,

Regards,  Nena
BFC and Local Tutor for NCT UK