Trailing by 13 points to Sudbury midway through the second half, it looked certain that their celebrations would be on hold for at least another week.

But four late tries earned Colchester a thrilling 51-42 win, and as the players celebrated on the pitch news filtered through that second-placed Letchworth had lost at Southend, confirming The Blacks’ promotion with two matches to spare.

“It’s crazy,” said captain Cam Kerr. “I didn’t expect it today. To get it done now is incredible.”

And crazy is an appropriate description of the 15-try roller-coaster which unfolded in front of one of the biggest crowds of the season.

The match started with little indication of the drama to come, as Colchester raced into a 14-0 lead thanks to well-taken tries by Ardal Yallop and Fin McCartney, Gabe Jones converting both.

Sudbury, backed by their usual vocal support, hit back, scoring with their first proper attack through Frazer Beckett, the scrumhalf’s try converted by Cam Greenhall.

With Callum Jeffery on for Francois Rossouw, Colchester went further ahead, a line-out from a penalty resulting in a maul and the ball breaking right to Jacob Bodkin who scooted over.

Just after the half-hour, Sudbury had their second, a patient build-up leading to Gabriel Holland crossing for a converted try.

Greenhall’s misdirected cross-field kick went straight to Bodkin who raced in for his second and Colchester’s bonus point, only for the wing to leave the field to be replaced by Ed Parry.

A lovely length-of-the-half move involving most of the backs ended with a score for Kerr, and with a 29-14 lead at halftime Colchester looked comfortable.

Then came an extraordinary 20 minutes as Sudbury scored four eye-catching tries, their dangerous backs running riot.

First Jake Sumner scored a length-of-the-field effort, then his centre partner Austin Beckett chipped in with two tries, as Colchester’s defenders were left grasping at air.

The visitors’ sixth try was scored by wing Nath Atherton, and inevitably all the scores were converted by the impeccable Greenhall.

Suddenly Sudbury were 42-29 up and Colchester looked up against it. But now it was turn of the hosts to score four unanswered tries of their own.

First replacement Danny Whiteman went over in the right corner, then five minutes later Ben Kelland crossed after a patient build-up.

Colchester sneaked ahead through Findlay Gilmour’s try, before McCartney made the game safe from a lineout drive five minutes from time, his second try was converted by Louis Martin as both Henry Newman and Jones were off the field injured.

“Fair play to Sudbury for coming here and wanting to play,” said head coach Mike Haywood. “But credit to the boys. They just kept fighting and fighting. It shows the character of this group.”

Haywood described clinching promotion as “awesome” but is now setting his sights on finishing the season unbeaten.

“We’ve got two tough challenges coming up, starting with Amersham who are fighting to stay up. It would be amazing for us to go up unbeaten, but we know how tough that’s going to be.”

Will Blakemore was named player-of-the-match by sponsors Matthew Douglas, while the coaches’ award, courtesy of the Lexden Crown, went to captain Kerr.

Elsewhere, the Ravens lost 48-40 at Ely while the Cavaliers won 43-22 at Thurston.