I think that you will find that this was Union Church. I know this from the 1950s as I attended the Scout Troop that used to meet in Union Hall that was known as the 35th Brighton.

It looks like the Union Church to me too. It used to stand on the corner of Air Street and Queen's Square. Fond memories of going to jumble sales there as a kid in the 70s.

Central Union Church, demolished about 1985 I think.

There are several photos and more information re this church and surrounding area in the wonderful James Gray Collection (Volume 21). Cheers

It's a common mistake to call the Square alongside the Union Church 'Queen's Square' but the traditional name for this (far from square) square is Queen Square. The mistake is so common, and understandable, that it might be considered to represent a change by popular demand.

The Union Hall on a Saturday night in the mid 1970s also became a great venue for young bands to hire who couldn't get gigs of their own. Does anyone remember So and So's Travelling Whatsits with future Pirhanas in their ranks, High Priestess, Senator, Bean Machine and even Freeway? It was rough and ready and very affordable. Some bands had thunderflashes that went off, not during crucial dramatic moments in a song but when they were tuning up!

The Union Church Hall was also used by Brighton Arts Theatre Group to perform their plays.