The defeat allowed Tunbridge Wells to pip them at the post, courtesy of their 46-14 home win over Maidstone.
Senior coach Will Knight praised his side’s effort despite them coming up short.
‘The final scoreline flattered Sidcup and it was a good battle all the way through,’ said Knight.
‘There was only eight points in it with 25 minutes left.
‘Because we had to go for it, that left gaps for them to exploit.
‘We threw everything at it and didn’t come away with any regrets.
‘Sidcup were just that bit more clinical in front of a large crowd and are worthy champions.
‘We were forced to make a number of changes due to injury and unavailability, but all the players gave 110 per cent.
‘We knew we faced the toughest possible task and said way back the last thing we wanted was to have to go to Sidcup on the final day needing to get something.
‘As a side, it is earlier defeats we have to reflect on as to where we slipped up.’
Havant couldn’t have wished for a better start and opened the scoring with a Darren Bamford try – the first of a hat-trick for the full-back.
Jason Rudder made a good break and Bamford crossed out wide.
Outside-half Jacob Knight, in for injured brother, Joel, added the conversion.
Sidcup hit back to lead 17-7 with a penalty and two tries but the visitors soon regained their advantage.
Knight knocked over two penalties in the space of four minutes and then fielded a Bamford cross-kick for a try he converted himself.
Havant conceded a try on the stroke of half-time, leaving them 24-20 in arrears at the break.
Two tries in the opening 20 minutes of the second half saw the hosts stretch their lead to 38-20.
But Havant went down fighting and grabbed two of their own.
Right-winger Harry Carr scored the first and then Bamford completed his hat-trick.
Though the gap was just eight points, Havant were still chasing the game.
Eventually Sidcup pounced on a dropped pass to kill off the remaining hopes the visitors had off getting a positive result.
‘It was a brilliant effort,’ Knight added.
‘The club can look back on a successful season.
‘We remained unbeaten at home, retained the Hampshire Cup and our second and third teams won their respective competitions.
‘Players want to play for us and spectators turn up in big numbers.
‘We are in rude health. The aim is to get back into the National Leagues.’