20 foot is not a small trailer its a big one and should have come fitted with brakes as standard. Was it a genuine one or one which someone cobbled together. If it weighs more than 750 Kg then it MUST have brakes by law. And dont assume its not that heavy get it weighed, cause the boys in blue will.
http://www.dft.gov.uk/pgr/roads/vehicles/vssafety/requirementsfortrailers
B
September 2008