Hi Wango- I think you will find that most sites in France and Spain use the standard blue plug for hook up, as in the U.K. If you dont want to take any chances, then buy a short lead 2 pin continental plug for the very rare occasion you may come across this.
What may be of interest to you also is to purchase a polarity tester, this will let you know the state of the wiring system of the site, continental sites sometimes have the live/nuetral the other way round than in the U.K. The polarity tester pluged into the van 13amp socket will tell you if this is the case.
There is a great offer on today 15th july at Aldi stores which are selling these at just £2.99. I also made up myself a short lead reversed cable, simply connect the live to the nuetral connection and nuetral to the live connection.
If you are unsure about this then I think you may well be able to purchase these at a decent caravan acsessory shop, making sure that you lable this lead for what its function is.
Have a great trip away from rain soaked U.K.