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We explore trends in the morphology and line-of-sight (los) velocity ofstellar populations in the inner regions of disc galaxies, using N-bodysimulations with both a thin (kinematically cold) and a thick (kinematicallyhot) disc which form a bar and boxy/peanut (b/p) bulge. The bar in the thindisc component is $\sim$50\% stronger than the thick disc bar and is moreelongated, with an axis ratio almost half that of the thick disc bar. The thindisc b/p bulge has a pronounced X-shape, while the thick disc b/p is weakerwith a rather boxy shape. This leads to the signature of the b/p bulge in thethick disc to be weaker and further away from the plane than in the thin disc.Regarding the kinematics, we find that the los velocity of thick disc stars inthe outer parts of the b/p bulge can be \emph{larger} than that of thin discstars, by up to 40\% and 20\% for side-on and Milky Way-like orientations ofthe bar respectively. This is due to the different orbits followed by thin andthick disc stars in the bar-b/p region, which are affected by the fact that: i)thin disc stars are trapped more efficiently in the bar - b/p instability andthus lose more angular momentum than their thick disc counterparts and ii)thick disc stars have large radial excursions and therefore stars from largeradii with high angular momenta can be found in the bar region. We also findthat the difference between the los velocities of the thin and thick disc inthe b/p bulge ($\Delta v_{los}$) correlates with the initial difference betweenthe radial velocity dispersions of the two discs ($\Delta \sigma$) . Wetherefore conclude that stars in the bar - b/p bulge will have considerablydifferent morphologies and kinematics depending on the kinematic properties ofthe disc population they originate from.

Bars & boxy/peanut bulges in thin & thick discs: I. Morphology and line-of-sight velocities of a fiducial model