When Microsoft launched the Surface Pro 4 they also released a new Type Cover which included a Fingerprint reader which is great with the Surface Pro 3 for Windows Hello as the Pro 3 doesn’t have the RealSense camera for automatic logging in. The only problem was the new keyboard was only available in the US until now. You can now pre-order the keyboard which will ship March 15th. Even though it is listed as a Surface Pro 4 cover it will work with the Surface Pro 3.
The Type Cover costs £134.99 from the Microsoft Store.