Context :

Aims : We contribute to improving the census of cool brown dwarfs ( late-T and Y dwarfs ) in the immediate solar neighbourhood .

Methods : By combining near-infrared ( NIR ) data of UKIDSS with mid-infrared WISE and other available NIR ( 2MASS ) and red optical ( SDSS z -band ) multi-epoch data we detect high proper motion ( HPM ) objects with colours typical of late spectral types ( > T5 ) .
We use NIR low-resolution spectroscopy for the classification of new candidates .

Results : We determined new proper motions for 14 known T5.5-Y0 dwarfs , many of them being significantly ( > 2-10 times ) more accurate than previous ones .
We detected three new candidates , ULAS J0954 + 0623 , ULAS J1152 + 0359 , and ULAS J1204 - 0150 , by their HPMs and colours .
Using previously published and new UKIDSS positions of the known nearby T8 dwarf WISE J0254 + 0223 we improved its trigonometric parallax to 165 \pm 20 mas .
For the three new objects we obtained NIR spectroscopic follow-up with LBT/LUCIFER classifying them as T5.5 and T6 dwarfs .
With their estimated spectroscopic distances of about 25-30 pc , their proper motions of about 430-650 mas/yr lead to tangential velocities of about 50-80 km/s typical of the Galactic thin disk population .

Conclusions :