Here in the UK, despite strict laws saying otherwise, they really don't care what you carry in your vehicle as long as it doesn't go bang. Any type of firearm is a complete no no. Baseball bats, Machetes, carving knife. The most that is likely to happen, unless actually used in the wrong way, would be confiscation of said article.
As much as I love firearms and would carry one if legal to do so, in my 60 plus years I have never experienced a situation where I wished I actually had one on my person whilst travelling.