The safe towing limit in terms of stability is advised by the main caravan organisations as 85% of kerbweight. So first of all establish your kerbweight, multiply that by 0.85.
Megane 1.6 Sport Tourer >06 has a listed weight around 1260kg, so 85% of that would be 1070kg. From 06 onwards the wight increased to 1315kg so your 85% would be 1117kg. To make things more confusing caravans have two different weights, the "ex factory weight" or MIRO (mass in running order), effectively the unladen weight, and the Maximum Permitted Total Laden Mass or MPTLM which is the laden mass. It is always the laden mass you should refer to.
The second consideration should be how well the car will cope with the weight on the back, and the best resource to establish that is What Towcar's web site which allows you to estimate how well you can expect your car to perform, whether it will cope with hills and especially hill starts when towing a caravan.
The third consideration is wear to your car. The manufacturer will issue a maximum towing limit for your vehicle to protect the engine, gearbox and clutch from damage. This may be higher than the 85% of kerbweight. You always use the lower figure as your absolute maximum. Bear in mind that the closer to the manufacturers limit you are the more quickly you should expect key vehicle components to wear.
You should also look to increase the frequency of engine and gearbox
changes whenever you use a car to tow a caravan.