In the UK the front line and entrance attendants are required to be SIA certified this year. These are trained security personnel and approved by the police/government. There are lots of brothers, mainly Eastern European, who have this registration.
Last year excel exhibition for the RC was full of SIA attendant. Apparently someone went on stage, and these were the only attendants allowed to remove him
If they can not provide these people, then they have to ask the venue to hire them.
The good thing, is most SIA certified will have liability insurance, so if something goes wrong, WBTS will not have to for fork out any money. The insurance will pay.