score:9
I've done this all over the world without incident. Just make sure your devices are ok with the voltage coming from the wall, and that you're not throwing away grounding protection by using a two prong adapter instead of one with a grounding strip.
To check voltages, I use Wikipedia. In your case Spain and the UK are on the same voltage, so that's not an issue.
This kind of adapter for Spain:
is not grounded. If you use this to plug in the power strip, the devices won't have grounding (earthing) protection.
This kind of adapter for Spain:
is grounded (though you need a different face on it for a UK plug instead of a US one.) These larger ones are better for plugging in a power strip.
Upvote:1
If everything you want to charge is USB compatible you can use something like this http://www.amazon.com/Photive-Desktop-Charger-Intelligent-Technology/dp/B00LMIA9L4/ref=pd_sim_cps_5?ie=UTF8
Recently did a Eurotrip with the family in various countries and it charged 3 phones, 2 IPads and a Kindle Fire nicely. You only need to bring one outlet adapter for each different style (UK, Western Europe, US).
Upvote:2
You won't have any problem: voltage is the same and if you're only planning to plug chargers they require very little power so no issue there either
Upvote:4
Avoid doing this and you will be safe :)