  TeV BL Lacertae objects require extreme relativistic bulk motion in the
gamma-ray emission region, but at the VLBI scale their radio knots hardly move.
The same sources show evidence, in radio, of a structure made of a fast spine
plus a slow layer. We propose that this structure exists even on the spatial
scale of regions responsible for the gamma-ray emission. One component sees the
(beamed) radiation produced by the other, and this enhances the inverse Compton
emission of both components. In addition, this allows the magnetic field to be
nearly in equipartition with the emitting particles. The inverse Compton
emission of the spine is anisotropic in its frame, possibly producing the
deceleration of the spine by the Compton rocket effect. In this scenario, also
the slow layer is a relatively strong high energy emitter, and thus
radiogalaxies become potentially detectable by GLAST.
