Contrary to t__m__i's suggestion, I wasn't plotting some bizarre trip round Europe, I was trying to work out whether there were any places in France with trams / metro systems apart from Paris, Lille and Valenciennes that one might plausibly go on day trips to by public transport. The answer appears to be yes, kind of. One can get to and from Reims if one gets up very early (essentially the first train from Didcot Parkway). There is a TGV to Reims, well two actually to different stations, but the connections aren't as good as one might hope. The other alternative is to drive to and from Poole and get some sort of boat to Caen - they are reasonably fast. However, it would be a long day and 'he died driving back from Poole having gone on a day trip to Cean to look at their rubber tyred trams' is not the way I want to go. Yes, rubber tyred trams, http://en.wikipedia.org/wiki/Caen_Guided_Light_Transit - seems the best description to me of what they are.
[ETA - the second one of these is wrong, see comments]