Your shareholder certificate is held online on Computershare's Investor Centre.
Please note, no written documentation or certificates are sent in the post.
In order to access it, you'll need to register an account with them here: https://www-uk.computershare.com/investor/registration.asp
You will need your shareholder number and your Postcode (if within the UK) or domicile Country.
By registering this will trigger an activation code sent by post. Unfortunately this process is non negotiable per Computershare.
Once you have the activation code you can complete the registration and access your certificate via the 'My Documents' section.