I hear where you are coming from One Track, having lived in Perth for a couple of years.
However,unlike WA, in the UK a trailer does not need a licence.
Separate insurance is also not needed for a trailer or caravan.
(although I would like caravans taxed at £500 a year :-) )
Despite the trailers appearance it appears to be an old horse box chassis which is quite substantial.
It is highly unusual for such minor motoring offences to result in being held in police cells and brought before magistrates the next day.
Such 'offences' are normally handled at the roadside with a ticket.