It's based upon what the bank thinks it is worth. Which is likely closely related to what you are paying for it and what similar properties in the area have sold for.
@Zerostar started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
It's based upon what the bank thinks it is worth. Which is likely closely related to what you are paying for it and what similar properties in the area have sold for.