Term for a booking with two escorts at the same time, often with lesbian interaction between the girls. Also called MFF. This is in breach of the UK's archaic brothel laws although neither you nor they are breaking the law unless any of you are classed as being in charge of the building and therefore the 'brothel keeper' - you if its in your home or them if it is in their home or flat. The only way to get round this would be by booking a duo in a hotel - the hotel would not be breaking the law as long as they did not allow the activity. See Brothel Laws for more information.
No UKP member has reported being arrested nor 'spoken to' for this technical violation.