Sadly I was on last night when this happened. It was definately a nightshift I want to forget.
I dont know exactly what happened there but I'll give some insight into what USUALLY happens, from experience.
1) People arrested in the street are normally handcuffed to the front or back and are searched under Section 32 of PACE prior to entry to a police car or van.
This search is for any articles used to evade custody or pose a risk to the officers, and the like.
2) Upon arrival to the custody suite, some officers will remove handcuffs on arrival, based on the detainee's demeanor and offence arrested.
3) Whilst at the custody desk, some sergeants authorising detention will tell the arresting officer to remove handcuffs PRIOR to the secondary search in the custody suite. HOWEVER, this will again be based on demeanor and whoever the custody sergeant is.
I don't know exactly what happened last night, but all signs are pointing to the arresting officer not conducting a satisfactory search, and a colleague of mine paid with his life because of it.