You do not need a flashing switch for MOT. BUT you MUST have a flashing warning lamp somewhere which indicates that the hazard lights are ON!
The Frontera A has this on the dash in amongst the warning lights... it's a flashing triangle pic which is to the left of the normal indicator lights, if anyone wants I can get a pic of it later, but you've all got one so it's not really needed.
If you have rewired the hazard then yes, must flash with or without ignition, and must have a light inside the vehicle which indicates they are on... as such on dash where the original is, or get a flashing switch as shown by several people.
Cheers,
Si