Technically possible.
More often bricking up the party wall is a mortgage condition imposed at sale.
The reason is fire can spread easily from house to house in a terrace row and has in the past lead to several houses burning down/damaged due to fire from a neighbouring property. It’s not so common in modern times due to having a proper fire service, many being bricked up/partially bricked up, decline of fire causing habits and incremental legislation which has meant homes are much safer now than they were in the past.
Many terrace houses, turn of the century and older didn’t have fully bricked up party walls, I’ve seen them where they run an entire blocks length.
You can brick it up yourself. It doesn’t require decent brick laying skills as said masonry is not on show! It is common to use the cheapest blocks concrete or aerated, single skin, especially aerated as they are easier to handle/lay, cover a larger area per unit and can be easily cut to the pitch of the roof with a sacrificial hand saw! You can use other methods as long as it is fire proof.
It is not unknown for it to be hidden by rooms in roofs and or getting rid of the loft access trap so it can’t be inspected in the first place 😆