I drive to Kent (from Brighton) every now and then and coming back (past Dover) there are hundred of French/German/Italian cars and they do just fine on our roads, so why should we be any different?
OP, it'll be perfectly fine.
pffft having driven a rhd in paris i will tell you its hard as nails however on a motorway all you need do is hang back, plan ahead and its not so hard to overtake or anything. in france anyway you have to be semi aggresive otherwise you get nowhere mind. you got to get the balance right. would never try italy in a rhd though. good lord they are insane
I drove my, RHD, car for 5 months last year when i was at home in Denmark and it was pretty much exactly the same as driving in the UK. Obviously there is a slight disadvantage when overtaking on a single lane but not one that was dangerous as long as you keep an adequate distance. Plus parking was easier in the city.