If you are need the local toilet block is here for you during normal working and daylight hours. They are kept in a reasonable condition for the town and are safe to use at all times (unless being cleaned).
They are close to the centre of Shefford town on Northbridge Street almost opposite The Lemon Tree beauty treatment salon next to the old Jubilee Fire station.
If the toilets are closed please ask nicely at one of the local public houses and I'm sure they will oblige. You might even find yourself staying for a quick one.