When the lender is confident that you will be able to repay the mortgage, and is satisfied with the valuation report on the property and the results of legal searches, it will issue a formal mortgage offer (known as an "offer of advance").
Certain conditions may apply to the offer of advance. For example, if specific work is needed on the property the lender may:
offer to provide the full amount of the mortgage when you buy the property as long as you carry out the work within a certain time; or
offer only part of the loan at first, paying the rest when the work has been carried out. The money held back is called a "retention".
If you want to go ahead and get the mortgage to buy the property, you must accept the offer of advance. The legal work then needs to be completed.