FFI charges apply to any organisation that receives a notification of contravention from a HSE inspector confirming that a material breach has taken place and must be rectified. It is essentially the HSE charging a fee for the time it spends identifying, addressing and resolving an organisation's health and safety breach(es) and will usually include the time spent on the entire original visit. It can also include the time spent preparing a report, speaking with you and your workers, and obtaining specialist advice.
HSE's reasoning for the increase in FFI is that in recent years they have been operating at a deficit, with the HSE's cost of dealing with material breaches being more than they have been able to recover. The increased FFI aims to allow the HSE to recover its full costs, along with taking into account cumulative inflationary pressures. In addition, the increased FFI should also act as encouragement to organisations to ensure that they are proactive in complying with health and safety law, as non-compliance now has more significant repercussions.