You could use adaptors all over the place: yes there is a safety problem with this. The more adaptors you use, the higher the possibility of shorts (as an adaptor is supposed to be a temporary fix- not for permanent use) and thus- power outages or fires or ruining your appliances.
As far as the washer- I don't know about the UK- but I know the washers (although take longer) are more energy and water efficient than in the US- you may want to take that into consideration since drought and conserving water in spain are big issues.
In the UK you guys also usually have larger living quarters than in Spain- so what you have you'll have to be sure will fit wherever you're going. If you're renting chances are the place will have a washer already.
As far as if you've already bought them- if you were planning on moving, its never a good idea to purchase such items until you know where you're going what you'll need, what is really necessary. Consider selling them and purchasing again in Spain- I don't know how new/old the items are, but its something to consider.
Good luck with your move!