After a eight-game unbeaten league run, the Middle Road outfit appeared to have pulled clear from danger, but they have followed that with three straight defeats to remain on the fringes of the relegation scrap.
All three of the losses have come against sides in the top half of Division 1, but they never got going against Lingfield going down 3-1, and Burt labelled their performance as woeful.
He said: “We were terrible from minute one, we didn’t turn up and got exactly what we deserved.
“It was mistake after mistake and a very bad day at the office.
“Their goalkeeper was a reserve midfielder as I understand but we never tested him and there can be no excuses, we were woeful.
“We’re not safe yet, all the sides around us will pick up points and we’ll have to win four of our last seven games to be sure of staying up. They’re all tough games, so I’m expecting a response as that was not good enough and we let the players know it.”
Shoreham were poor from the opening moments and it was a loss of concentration that allowed Lingfield to go ahead after three minutes.
Tom Hughes played the ball out of defence, Lee Flavin ran onto it and his long ball forward caught out Mussels keeper Sam Armfield, bounced over his head and in from 25 yards.
Whether Flavin meant it or not was a matter of debate, but the opener unsettled Shoreham and Lingfield, sensing this uncertainty, almost added a second through Daryl Coleman.
Josh Clayman fired over and Kevin Keehan dragged an effort wide in a brief Shoreham flurry but the visitors went further ahead through Josh Coulson, who slotted home a penalty after Armfield had sent Simon Wallace tumbling.
Shoreham simply never got going and fell 3-0 behind through Wallace on 58 minutes, when Coulson and Coleman linked up to play him in.
Debutant Ollie Hartley, signed from Eastbourne Borough and Mussels’ best player on a tough afternoon, flashed an effort over while, at the other end, Harry Sintim shot just off target.
There seemed no way back for lacklustre Mussels, but they were given a glimmer of hope on 74 minutes when Clayman went down under a challenge from Flavin, who was then dismissed either for the initial foul or the protestations that followed.
Owen Callaghan sent stopper Rhys Oscar the wrong way from the spot, but that was as good as it got for Mussels.
Shoreham remain in 14th place and six points above the relegation zone.