I do corporate leasing for fleets of 50 and above.

Most of the cheap deals advertised are non-maintenance, 10,000 miles (or less) per annum, and on spread rental payment profile like 6 in advance followed by 35 (ie you have the car for three years but pay 41 instalments.)

It's important to realise that anything with a balloon payment to give you ownership at the end is NOT a lease. It is HP by a multitude of names.

Second, A proper lease will have VAT on the rentals and while VAT registered businesses can recover some or all of the VAT on the rentals, private individuals can't so it is immediately 17.5% more expensive.

If your business is a Limited Company and you are a Director or employee, you will have to pay Benefit in Kind tax on the car, and your business pays NI on the value of the BiK. (Remember that the self-employed can be VAT registered and they have different BiK rules)

As for depreciation, in simple terms, the rental you pay is calculated as follows:
Depreciation (ie Cost to buy the car less expected Residual Value)
+ interest on the debt for the period
+ Maintenance charges (generally NOT included in the cheap rates mentioned above)
+ Road Fund for the period (watch out for future increases)
+ Lessors overhead costs
+ Lessors profit

If the leasing company get the residual wrong that is their problem when you hand the car back, but remember that you may have to pay excess mileage or refurbishment charges.

This is a long-winded way of saying that you shouldn't be seduced by a low front end cost or think you are buying anything - on a lease you are only paying for the use of the car. If you are happy with that and the numbers stack up for you, fine. If not, a more traditional funding method might be better.