"Many of the rules in the Code are legal requirements, and if you disobey these rules you are committing a criminal offence. You may be fined, given penalty points on your license or be disqualified from driving. In the most serious cases you may be sent to prison. Such rules are identified by the use of the words MUST / MUST NOT. In addition the rule includes an abbreviated reference to the legislation which creates the offence."
Signals
85: Signals warn and inform other road users, including pedestrians (see Signals to other road users section), of your intended actions. You should:
give clear signals in plenty of time, having checked it is not misleading to signal at that time
use them, if necessary, before changing course or direction, stopping or moving off
cancel them after use
make sure your signals will not confuse others. If, for instance you want to stop after a side road, do not signal until you are passing the road. If you signal earlier it may give the impression that you intend to turn into the road. Your brake lights will warn traffic behind you that you are slowing down
use an arm signal to emphasise or reinforce your signal if necessary. Remember that signalling does not give you priority.
I.e. "Signals are good - use them, properly, although you can't be prosecuted if you don't". --M-A
Other bits are:
155: Well before turning right you should
use your mirrors to make sure you know the position and movement of traffic behind you
give a right-turn signal
take up a position just left of the middle of the road or in the space marked for traffic turning right
leave room for other vehicles to pass on the left, if possible.
And of course:
158: Use your mirrors and give a left-turn signal well before you turn left. Do not overtake just before you turn left and watch out for traffic coming up on your left before you make the turn, especially if driving a large vehicle. Cyclists and motorcyclists in particular may be hidden from your view.
None of which use the magic MUST or MUST NOT words. - Admiral
Side of the Road
136: Once moving you should
keep to the left, unless road signs or markings indicate otherwise. The exceptions are when you want to overtake, turn right or pass parked vehicles or pedestrians in the road.
I.e. "Don't drive on the wrong side of the road". --M-A
Cyclists riding several abreast
143: DO NOT overtake where you might come into conflict with other road users. For example
when you would force another vehicle to swerve or slow down
I read this as "Don't cycle more than one abreast if it gets in the way of other traffic". --M-A
I read this as "Don't change to cycling more than one abreast if this gets in the way of other traffic". Other traffic doesn't have any right to overtake a cyclist (over 10mph) to my knowledge. Of course, being under 10mph classes you as stationary, which is never a GoodThing -- ColinT
Other traffic may overtake a cyclist in precisely the same conditions as it may other other traffic -- Senji.