Given that this is the case in many European countries, this is a frequently asked question.
However, as with many other things, England is the exception.
Effectively, furnished properties are not systematically more expensive than unfurnished ones. This is good news for those who don’t want to bring their furniture over. Instead, the price of the property is determined, much like with unfurnished properties, by location, the number of bedrooms, and all other regular criteria.
The fact that a property is furnished is not as relevant - if, at any given moment, the owner has decided to furnish their property, it will stay furnished for the rest of its rented life (unless it is agreed by special negotiation with the landlord that the furniture will be removed). In general, 1 or 2 bedroom properties are furnished, whereas properties that have more than 3 bedrooms are empty.
Lastly: the lease for a furnished property is the same as for unfurnished. There is no legal or contractual difference, except in the inventory which will list everything that is provided by the landlord.