In general, yes you do have to pay them. This should be at their normal rate of pay.
In some cases, employees can be “laid off” without normal pay if there is a specific term in their contract allowing the employer to do this. This sort of clause is widespread in some industries, but virtually unheard of in others.
When employees are laid off in this way, they are entitled to a statutory payment from the employer called a Guarantee Payment. The current rate is a maximum of £21.20 per day. Payment is limited to a maximum of five days in any period of three months. An employee must have completed one month's continuous employment in order to qualify for a Guarantee Payment.
On days on which a Guarantee Payment is not payable, employees may be able to claim Jobseekers’ Allowance and employees should contact their local Jobcentre to see if they qualify.