Holiday pay should take into account the amount of wages an employee would usually receive, not just their contractual salary. This was effectively the finding from last year’s employment tribunal and the UK Government have been reviewing the findings; we do not know when to expect the final ruling.
The government is taking steps to try and provide some certainty and limit the impact on UK business. The current proposal appears to be a transition period of six months, and then claims cannot be backdated more than two years.
The UK Working Time Regulations will need to be interpreted in a new way, or changed. But it seems that things will change, we are just not quite sure what the changes shall be. If you want more information on the current proposal see here.