https://publicapps.caa.co.uk/docs/33...RO-FTL-110.pdf
This is the best that I could find. Basically, it’s up to operators to ensure that their rosters and any commuting plan that is followed is deemed to be in an FMRS secure way. So it’s not the CAA - it’s up to the company to decide.
“While commuting/travelling time is the crew member’s responsibility, operators should be aware and acknowledge its potential impact on their operation. Some airport locations are likely to increase the commuting time even where the crew member rests within 90 minutes of their place of report. Operators should consider what they can reasonably do to meet their responsibilities where they know or believe the crew member will be too fatigued to operate safely; and where necessary establish protocols to meet these responsibilities”