  We present ALMA observations of the mid-J 12CO emission from six single-dish
selected 870-micron sources in the Extended Chandra Deep Field-South (ECDFS)
and UKIDSS Ultra-Deep Survey (UDS) fields. These six single-dish submillimetre
sources were selected based on previous ALMA continuum observations, which
showed that each comprised a blend of emission from two or more individual
submillimetre galaxies (SMGs), separated on 5--10 arcsec scales. The six
single-dish submillimetre sources targeted correspond to a total of 14
individual SMGs, of which seven have previously-measured robust
optical/near-infrared spectroscopic redshifts, which were used to tune our ALMA
observations. We detect CO(3-2) or CO(4-3) at z=2.3--3.7 in seven of the 14
SMGs, and in addition serendipitously detect line emission from three gas-rich
companion galaxies, as well as identify four new 3.3-mm selected continuum
sources in the six fields. Joint analysis of our CO spectroscopy and existing
data suggests that 64 \pm 18% of the SMGs in blended submillimetre sources are
unlikely to be physically associated. However, three of the SMG fields (50%)
contain new, serendipitously-detected CO-emitting (but submillimetre-faint)
sources at similar redshifts to the 870-micron selected SMGs we targeted. These
data suggest that the SMGs inhabit overdense regions, but that these are not
sufficiently overdense on ~100 kpc scales to influence the source blending
given the short lifetimes of SMGs. We find that 21 \pm 12% of SMGs have
spatially-distinct and kinematically-close companion galaxies (~8--150 kpc and
<~300 km/s), which may have enhanced their star-formation via gravitational
interactions.
