The Kray Twins entertaind many High Profile guests at various clubs through London. They would do this at times with great fan fair for publicity and also at almost zero attention in order to protect the agenda, Not only Vito Genoese but many other people. The Mafia had a strong hold in London at the time and frequently met with Reg ( not so much Ron) - Hollywood types often as well as prominent Politicians from all shores, mostly under the radar.

We will never know how many and all who, since most did not want to be Photographed or noted as meeting with them.
They would even be greated or met at times by Ron Kray, who would be documented as in prison at the time.
Reggie would have Ron escorted in and out of Prison while serving terms for meetings.