"The government has agreed to increase the number of LSTs by an additional 1,000 and to extend the trial by 5 years. This increase will take the number of LSTs from 1,800 to approximately 2,800 over the next 12 months.
Operators will be invited to bid for a share of the additional allocation, in the coming months.
Details on how to apply will be available soon."
Update January 2017: Source https://www.gov.uk/government/collections/longer-semi-trailer-trial