Shifting with the wrong hand isn't a problem - shifting if you have never driven a manual transmission would be a major problem.

If you haven't driven in the UK before, you might want to take a look at http://www.direct.gov.uk/en/TravelAn...code/DG_070202 - it's the rule book for driving on UK roads, and also includes 'best practice' at roundabouts - ie, what you are meant to do. If the roundabout has lights and well marked lanes, then it will be easy, otherwise I'd take a look, at least at lane and signalling protocols - the roundabout section is http://www.direct.gov.uk/en/TravelAn...code/DG_070338