An updated Guide has been published by the Senior Courts Costs Office. The guide reflects the many changes in general costs law since 2013 and includes, at pages 94-96, a specific section on assessments under the Solicitors Act.
It can be downloaded from the link below.
Courts and Tribunals Judiciary | Senior Courts Costs Office Guide 2018 is published
New version of guide replaces the 2013 version with immediate effect.
Or you can browse it here