If the rifle is actually a .303, it is a No 1 MK III, otherwise known as a SMLE MKIII:

Rifle has been sported. Stock has been heavily modified, beyond saving if someone wanted to restore to as issue condition. Even the buttstock has been sanded to require replacement.

Rifle is not worth that much on the open market, though a 1912 action is an early rifles. probably worth around 150 as a sporter or restoration project. That said as a family heirloom it is worth a lot, and if you hav kids you should write down the details of your fathers use, so that it will not be forgotten in a decade or more as is most common with family firearms.

Based on action markings:

That said the action markings indicate it is a rather uncommon .22 cal rifle. Specifically it appears to be a 1914 pattern , No 2 rifles, based on the line of text below factory markings. However the action might have been used to make a .303 sporter. the If the caliber is .22 rimfire and not .303 it would be worth a bit as a restoration project. Unfortunately I do not know enough about the .22 cal market to give you an estimate.