I am looking at travelling by train from my home in UK to Portsmouth (UK) to catch a ferry to Spain. The ferry would leave UK  on the evening of the day I set off from home and arrive in Spain the following day.

I would then travel in Spain and Portugal on the train using my Interrail pass. 

My return journey would be the same in reverse. 

Could I use my Interrail pass for these rail journeys in the UK even though I will be leaving / returning to UK on a ferry, not by train (such as Eurostar) ?

Many thanks 

Bob