Number 5 reception centre was a building in central London used by the military during Operation Golden Age after their declaration of martial law. People arrested for looting were taken there where they would be processed. If found guilty, they would be sent on to a detention centre.
The Third Doctor and Sarah Jane Smith were taken to Number 5 reception centre after they were arrested, having been caught with looted goods. They were processed alongside Lodge, who had been looting, and had their photographs taken. The Doctor's claims to be a scientific advisor to UNIT were dismissed.
Together, the Doctor and Lodge overpowered a guard, but the latter then turned on the Time Lord, hoping to slow his pursuers by leaving the Doctor and Sarah behind. The Doctor knocked Lodge out and left with Sarah, only for the pair to be recaptured attempting to steal the Land Rover that would take them to the detention centre, which they were then loaded on to. (TV: Invasion of the Dinosaurs)