"Almost all cannabis seized by police now comprises high-strength varieties, with outdoor-grown herbal strains and hashish barely found," The Guardian reports.
The news is based on researchers analyzing samples of cannabis seized by 5 police forces in 2015 and 2016.
They found almost all the cannabis (93.6%) was sinsemilla, also known as skunk. This is a potent form of herbal cannabis often grown in the UK in indoor "cannabis farms" which has been specifically bred to have high levels of tetrahydrocannabinol (THC).
Analysis of samples of the drugs showed a wide variation in the levels of THC, with an average level of 14.2% in sinsemilla, compared to 6.3% in resin, according to NHS.