The EastEnders actress’ was joined by David, who is currently on medication for cancer, at the bash that happened last Saturday night.
But it quickly took a turn for the worst when he was reportedly discovered unresponsive on the street, before being rushed to hospital.
A source told The Sun, “David seemed fine at 4pm on Saturday, but not long after that it became clear he wasn’t right.
“He was slurring and falling about. When they went on to the soap awards, he was a real embarrassment. At the time Gillian was furious. Then he disappeared.
“It was only much later that a passer-by saw him lying in the street and called police, thinking they’d seen a corpse.”
David was then rushed to hospital and it was then that doctors discovered high levels of Rohypnol, often associated with drink spiking in his blood.
The source added, “Given he was on cancer medication, he was incredibly lucky it wasn’t more serious.
“The police are treating this very seriously because for a man with David’s health problems, the outcome could have been far worse than it was.”
The couple, who have been engaged since 2013, are said to be “horrified” that somebody could do such a thing, and it’s made worse by the fact they were in the company of friends that night.
“They were in company they trusted so it is shocking that this could have happened,” the source finishes.