Sue,
I just looked at the map on the bbc news website (
http://news.bbcimg.co.uk/media/image...ts_tues464.jpg)
If it makes you feel less worried, all areas, except the central London one, are all so so areas (except maybe Bromley but then not well known with that town). I lived in London for 10 years and to be honest, all those areas highlighted on the map wouldn't be places I'd go in the evening. According to a friend of mine in London, most of the trouble is caused by known thugs who are actually preplanning the places they will cause chaos via social media such as FB and Twitter, and via mobile/cell phone.
If they stay away from areas which are considered so so (and if they have been in the UK for awhile they will know what areas they are) they should be ok :)