A family offset mortgage is almost identical to a traditional offset mortgage. But rather than linking your own savings to your mortgage, you use those of a close relative. You use their savings to “offset” your mortgage debt.
For example, you want to buy a £200,000 property but do not have the funds for a deposit. Your mother, however, has £30,000 savings. Providing her savings are held with your potential mortgage lender, you could use them as your deposit. This is the equivalent of a 15% deposit and you would only need to borrow £170,000 to buy the property.
Not all lenders offer this type of mortgage. Of those that do, the family member must be immediate family – a long lost cousin, twice removed will not suffice.
Family springboard mortgages are very similar to family offset mortgages.
Family link mortgages are also similar, but they're instead secured against a family member's house rather than cash in a linked account.