The Information and Consultation of Employees Regulations 2004 (ICE) do not define who might be considered genuine representatives of the employees for the purpose of negotiating an agreement. The Regulations do state that all employees must be involved in the appointment or election process and must be represented by one of those elected or appointed. Employees must be allowed to nominate candidates from across the whole workforce and to vote in the election.
It's the employer's responsibility to enable ballots to take place. The ballot can be a single ballot, or separate ballots for different parts of the workforce, if the employer believes it would result in better representation.
The ballot process must be confidential and the ballot window must be open long enough to enable employees to be able to participate. In one case, a five-day window for a ballot by email was criticised by judges for being too short.