New car for a newbie tower

Are you sitting comfortably?

You need to note the MTPLM shown on the data plate on the caravan. Assuming you don't overload the caravan, this is the load which you have to tow, so you need a car which can safely and legally tow that load. Find a car with a kerb weight at least 15% more than that, and a manufacturer's towing limit greater than that. When you have done all that, make sure the car can handle a nose weight equal to the nose weight of the caravan (about 6% of the caravan MTPLM).

Assuming  your licence permits you to tow the MTPLM of the caravan plus the plated maximum Gross weight of the car, you've cracked it.

Coming back to your question about engine size, because the design of engines varies so much, and especially with the recent trend  towards smaller capacity but higher power and torque engines, you need to look at each car on its merits. You need an engine which develops enough power and torque at 60mph road speed in top gear. That may be 1500rpm or so if it's a diesel or much higher rpm if it's a petrol powered engine.

In the space available here, it's not possible to go into any more detail. There are umpteen finer points which can be made, but that's the jist of it.  My finger is dropping off.

Just Googled Bailey Orion 2 berth (2011) and a quoted MTPLM of 1076kg which is fairly light which will help with towcar.

But another thing to consider before moving the van - if it hasn't moved in a year please check the state of the tyres. If all the weight of the van has been on one spot on the tyre for a year it may well have deteriorated to an unsafe state - cracks in side wall and in tread may/may not be visible. there is also a date stamp on the tyre telling you how old it is - it's recommended that tyres shouldn't be more than 5 years old. Enjoy your caravanning. 

Given the weight of the caravan you have a very wide choice of tow cars probably anything over say 12 kg kerb weight with a towing capacity exceeding the MTPLM of the caravan will do but those with a towing capacity near the MTPLM will probably be sluggish and I would look at something with a bit more capability. For lightweight caravans the Skoda Yeti seems to be a favourite but your choice is vast.

You might also want to consider if the car will be kept longer than the caravan as if so something a bit bigger might be worth considering if it might have to tow something bigger.

I would agree that if it has stood for a year you need to check the caravan tyres.