Ferry to northern Spain, Santander
You can catch a ferry from the UK to Northern Spain. Ferries port in Northern Spain at Santander (the capital of Cantabria) and depart from either Portsmouth or Plymouth in England (Brittany ferries). Santander (Cantabria) is neighbour to Asturias on its eastern border.
There is also a ferry to Bilboa in the Basque country that departs Plymouth (P and O ferries), but takes about 36 hours and is a "ferry cruise".