Until 1953 the entire peerage attended a coronation ceremony. At that point, there was a total UK peerage of 936, including 736 members of the House of Lords, minors and peeresses in their own right.
In a statement to the House of Lords on
27 January 1953 the then Lord Chancellor rejected the view that every peer enjoyed an “absolute right” to a seat in the Abbey. Rather he was:
convinced that it lies entirely within the Royal Prerogative or otherwise within the personal power of the Sovereign to determine what Peers shall be summoned to the Abbey and what services shall be rendered by them; and it would be clearly improper in this House to challenge or criticise the exercise by the Sovereign of such powers.
The Lord Chancellor also reminded peers that their homage had been curtailed after 1902. Instead, 910 peers were accommodated (via a ballot) in the Abbey. If unsuccessful, a peer and his wife were entitled to a free seat in a covered stand to be erected outside.
https://researchbriefings.files.parliament.uk/documents/CBP-9412/CBP-9412.pdf
So they started in 1953.