Some of the things you want to do fall under the permitted development allowances others require planning permission which you would be very unlikely to get if you applied. If you apply and after refusal try to just do the permitted stuff you will find they scrutinise your development in more detail such as making you apply for building regulation approval on the drains etc
Also placing the van in your front garden is a recipe for disaster as the neighbours will complain and the planning department will feel obliged to do their best to stop you
Advice if you can do this
Use a crain if necessary to put a vehicle complying with the above caravan act in the back garden
Do not assume that someone selling you a cabin or modified carriage is being truthful when they say you don't need permission. For example, many suppliers are saying you don't need wheels. You can interpret the rules this way but alternative interpretations are possible that would need to be resolved in the high court which you could not afford. I would never assume that anything which did not have wheels and the ability to steer i,e, not a railway carriage would be compliant
If you are renting out as many people do you must be able to afford to stop doing this as any use must be ancillary to the main house and not separate so you may be stopped at any moment.
Do not rely on the income as it could be stopped very quickly leaving you with fines from Airbnb
Renting it out is a change of use and certainly not allowable although many people do this for years and get away with it.
If you can do it consistently with lots of lettings for over 8 years It may become legal
Good luck
Ted
