You can interrupt a split daily rest period the same as you can interrupt a regular daily rest period, you can interrupt either or both parts of a split daily rest period, so doing 14 hours which includes a 3 hour rest period then interrupting the daily rest period is legal.
For confirmation see the link at the bottom of this post.
Mazzer2:
I have done this on several occasions and was stopped the morning after in Kent having come down from Holyhead DVSA man asked for an explanation and said by rights I should have had 11 hours but as I didn’t appear tired he said he could see no point in parking me up. I told him that the tacho had said I was to good to go when getting off the boat to which he replied “Don’t always believe the tacho”. The fact he let me go makes me think it is maybe a grey area because if it was black and white he would have parked me up and fined me, this was mentioned before on here on a thread last year and someone else said they were doing it and had been stopped in Europe and there were no comebacks.
Better still believe the tacho not the DVSA bod who told you that 
If you’re having a split daily rest period you can still interrupt the daily rest period twice with a total of 1 hour interruption, either part or both parts of the split daily rest period can be interrupted.
Obviously you met a DVSA bod who needs to read the DVSAs own literature 
gov.uk/guidance/drivers-hou … vers-hours
Scroll down to “1.4 - Daily Rest Periods” then scroll down to “Journeys involving ferry or train transport”