An interesting debate, and have to agree that the Highway Code is not the Law of the road, but more in terms of road safety advice, the law of the Road is the Road Traffic Act 1988, of which there is a very small part relating to cyclists, part 1 Chapter 52, item 28 if I recall. However, it is legal for cyclists to ride 2 a breast, however it is not advisable in view of narrow roads but no one exactly knows what is defined as a narrow road in terms of width of the road, my friends and I were cautioned when we were teenagers by a motorcycle cop, (When Nottingham had them) that it is advisable not to ride 2 a breast on roads that don't have lane markings, one way streets and roads that exceed 30mph. The Institute of Advanced Motorists (IAM) of which I am a member of, now conduct road training for cyclists
http://www.iam.org.uk/cyclist. There has been some interesting debates of which the same advice is given to cyclists in the same view as Motorcyclists and that is ride defensively, keep left of centre, not left of the dotted lines, but left of the centre of the lane you are in. More and more cyclists are now using helmet camera's and there has been many successful convictions of "cage" drivers who drive without due care and attention due to submission of footage to the Police. Some very good examples on Youtube. I did my cycle proficiency in 1983 at the age of 8, and was taught not to go on the inside of lorries, as A), they need a wider turning arc to turn left and some trailers especially those that exceed 40ft have independent turning axles. B) The mirrors have blind spots, C) most of the indicator bulbs don't work. Same as cars, there are more blind spots on car mirrors than there are on HGV mirrors, which has been proved in the motorcycle press.