In the UK, the Highway Code is probably the most relevant for your purposes. It contains directions you must follow (which are law - like using lights at night) and guidance that it suggests you should follow (like wearing a helmet).
The Highway Code covers all road users - this section is specific for cyclists:
Also, can you by law ride in pairs? In what circumstances? Do you need insure to ride bikes in roads? Is the use of helmet mandatory?
Riding in pairs: “never ride more than two abreast, and ride in single file on narrow or busy roads and when riding round bends”
Insurance isn’t mandatory to ride a bike on the road - but lots of people will have 3rd party insurance (e.g. to cover their liability if they cause harm/damage to others) through membership of bodies like British Cycling.
Use of helmets: as above, advised but not a legal requirement.