You won't have any problem, as you are not leaving or entering the EU. The only time anyone will look at it normally is coming back into UK and it will still be valid then.

I brought one of my sons back from France on a passport a year out of date and all the official said was that it was o/d and it should be renewed.
Another son had to gain entry on a students union card as he had forgotten his passport altogether. (Not the most organised of people you may gather

)