A Disclosure of Incentives Form is a document filled out by the housebuilder/seller. The purpose of the form is to make sure that all of the financial and non-financial incentives offered to buyers are also clear to the mortgage lenders. This is very important as it may affect the value of the property.
This form was brought in because it was difficult for mortgage lenders to determine the true worth of a property. Say for instance a developer/seller offers a financial incentive of £5,000 cashback on their new build property, if the mortgage lender does not know this, they may value the property at £250,000 when a buyer is only actually paying £245,000.
In the above example, the buyer may find themselves with a mortgage that is actually worth more than the property's value. So, in short, this form is really beneficial to the buyer and the mortgage lender to ensure a fair price is being paid.