According to a report from Music Radar (https://www.musicradar.com/news/top-guitar-and-music-tech-firms-raided-in-price-fixing-probe) five major companies are currently being investigated by the UK Government’s Competition and Markets Authority (CMA). The investigation started on the 17th April 2018 and is expected to continue until autumn 2018.
The CMA report that the investigation is at an early stage and no assumptions should be made that competition law has been infringed. The press statement from the CMA (https://www.gov.uk/cma-cases/musical-instruments-and-equipment-suspected-anti-competitive-agreements-50565-2) doesn’t name the companies involved but according to the Sunday Telegraph (https://www.telegraph.co.uk/news/2018/05/27/guitar-maker-fender-four-japanese-musical-instrument-manufacturers/) the companies under investigation are Fender, Yamaha, Roland, Korg and Casio.

These are significant companies. Fender is one of the biggest names in the guitar world and produce the iconic Stratocaster and Telecaster amongst its range of electric and acoustic guitars. The other companies have a wide range of products from amplifiers to keyboards to various music tech.
Obviously, the process is just at the beginning and no one has been found guilty of anything yet, but these are major companies and any investigation will closely followed by everyone involved within the music industry within the UK.