Organisers were given their marching orders to make way for the civil ceremony – booked long before the political speech-making.
The Taxpayers’ Alliance had hoped to commandeer the civic gardens at Bridlington as a backdrop for much of the afternoon before learning of the double-booking.
More than 70 protesters turned up ready to vent their fury against council bosses accused of bungling the town’s regeneration.
But the campaigners had not bargained on the site being needed for a wedding taking place within an hour of the protest starting.
Alliance chief executive Matthew Sinclair and several others were able to deliver a stinging rebuke to East Riding of Yorkshire Council over its handling of regeneration plans for the town.
But after chanting “Justice for Bridlington” a couple of times, the crowd had to wrap it up so bride Anna Porecka could say “I do” to Martin Ryder.
The couple, both in their 50s, from Bridlington, had chosen the town hall to tie the knot in front of more than 30 family and friends.
The last demonstrator disappeared just as she pulled up outside the town hall register office which is inside the building.
The ceremony went ahead as planned and a family spokesman said after the ceremony on Saturday: “They just disappeared in time.
“It was a bit of an unfortunate coincidence.”
The new Mrs Ryder said she was not aware of the demonstration’s clash with her big day.
The protest, called “Justice for Brid”, was arranged last week after Tesco decided not to build a new store in the resort.
This would have freed its existing site for a new retail development that was a key part of plans to bring £200m of investment to the town.
Council bosses have said they are “disappointed” by Tesco’s decision.
Planning director Alan Menzies said the council remained committed to revamping the town.