Hi all I am considering buying a moped but was wondering if it is legal to ride it on a bypass with a max speed of 60/70 ?

I am unsure althouth I have seen Bicycles !!? using this bypass before…

is this legal ?

for
a) a 50cc moped to be used on the bypass

and

b) a bicycle to be used on a bypass?
Well I know that you can use a 50cc moped on normal roads where cars are allowed. but what Im asking is about on BYPASS roads only (I assumed ou could not ride your bike or moped n the bypass but I have seen a few people doing this before – just curious )