Unfortunately, there is no birth registration for a Peter W. Hayes in the Dec.qtr.1921 (or Mar.qtr.1922 if a late registration) anywhere.
There is, however, an entry for a Peter W. Hays in the Dec.qtr.1921 at Pancras (mothers maiden name Butler). Possibly the GRO mistranscribed 'Hayes' when indexing. I certainly can't find a marriage between a Hays and Butler although there a few between Hayes and Butler. The only way to determine if this is indeed your Peter would be to purchase the birth certificate to see whether the birth dates are the same.
Annette