...of a covert surveillance systems.
Nit-picking I know but you would expect that the mighty brains of the Civil Service could get the syntax right in an invitation to tender.
It could either be:
"of a covert surveillance system."
"of covert surveillance systems."
The original is sloppy, careless and unprofessional.
On the other hand it might just be a transcription error.
It's still doesn't look good even if it was.