What is the value of a webley and Scott mk1 air pistol patent number 219872 model number 19971?

The Mark I was made between 1926-29, apx 1500 were made. If you want an estimate of value then you will have to give more information about the condition of the rifle. Is it still working? what condition is it in. Poor, Fair, Good, Very Good or Excellent?

Without more information it is not possible to give you an estimate of value.