Thank you for your reply. We have tried, over the years all that you have said and more, apart from medication. Giving a treat is a very recent strategy.
We leave the house (barking begins), we stop just up the road in the car park, Chica jumps out for less than a minute, happily jumps back in, is given a pigs ear, no more barking till we reach our destination. Have run out of ideas apart from buying ear plugs!