After watching the (very good) english TV show Merlin, I read the King Arthur wikipedia page, and pretty much all related pages. And it's mentionned at the end, that the myth of Arthur has been used a lot by the british government during WWII. Unfortunately, there is no source for this claim.
I've been searching a little, but couldn't find anything. Do you guys have anything ?

Interesting to find out more on this.

Have known about Drake's Drum.

Wiki
Shortly before he died he ordered the drum to be taken to Buckland Abbey, where it still is today, and vowed that if England was ever in danger someone was to beat the drum and he would return to defend the country. According to legend it can be heard to beat at times when England is at war or significant national events take place.

interesting story

I think this is correct but haven't looked for anything.