Trouble with things like this is.. there's no still, video, or witnesses. Not that I am advocating such behaviour. I just like to be fair. If someone is doing this, then chances are someone will get the required evidence. LD65 LVF.. anything to say on this?
onlyme "cycling side by side which although allowed is blatantly abusing other road users".
If you bother to read the Highway Code, you will see it gives in rule 66 the situations where you should ride in single file: "never ride more than two abreast, and ride in single file on narrow or busy roads and when riding round bends". The road was not especially narrow / busy / bendy, so the normal maximum of two side by side would apply.
Any more alleged details?