yes but if your local authority has passed a by-law, or if there is a maintenance clause in your deeds, you can't. Also, if you inpede someone access or spoil their view or block their daylight you'll get a visit from the environmental health who will ask you to move it,
As long as it isn't blocking view/sunlight to surrounding houses or is in a unreasonable state to which could cause harm or danger to bystanders/people walking by the properly. That really is the only plausible reason for even suggesting it could/would be a problem.
If there is a covenant on your deeds preventing you doing it, then strictly speaking you can't. But if no-one complains, carry on. If someone does complain it's usually up to your local council to adjudicate, if I read it right.
Caravans aren't the nicest things to look at, so your neighbours may be less than pleased. There is a distinction between what you can do and whether you should do it.
On the estate I live on there is a covenant specifically banning keeping caravans on your property so you should check your deeds. I will add that this has not stopped the couple opposite me, whose caravan has been parked in their front garden for all of the 3 years I've lived here.