During my days working for Ford part of my job was dealing with organising trips from various interested parties around the Valencia plant (builds Ka, Fiesta and Focus) and the Bridgend enigine plant (builds all ford engines as well as the big Jag and Volvo ones).
Basically it was mostly from people in related companys who we let in (people from Jag, Mazda, PSA etc.) but when we got approched from an enthusiats club in Spain we let them have a tour.
I cant imagine that Renault would be too dissimilar, worth someone high up in the club asking though. Talk to Renault UK, they should be able to swing it.
Hope this helps
Tom (ex Ford UK employee)
PS. for those who noticed I know PSA isnt owned by Ford but they had a lot of dealings over the HDI / TDCi engine collabaration