OK so we weren't exaggerating about the rain. We left our partly flooded campsite and continued north on the 'romantic road' to Wurzburg, luckily the campsite there was on top of a hill. Despite the diversions everywhere we didn't realise how bad it all was till we reached Bamberg and bought a paper. Only to discover that a lot of south and east Germany and the Czech republic was under water.  So it began to look foolhardy to continue to Prague - besides we didn't want to see it with the worst flooding for 100 - 400 years depending on who you talk to.
Therefore we decided to move considerably further north, to Berlin in fact, where there was an indication of sunshine, or at least less rain. Like most of our plans on this trip, this didn't quite work, but this time in a good way.  Driving up, we were stuck for a couple of hours in a huge traffic jam caused by, you guessed it, flooding on the motorway, so we stopped earlier than planned at a place called Ferch, just outside Potsdam.  The weather has been perfect, the camping is by a large and lovely lake and it is an easy bus ride to Potsdam. So we have been here for 5 nights, drying out, sightseeing, cycling round the lake and generally having a holiday!
Next stop, Berlin - almost certainly.