You are not required to pay your employee whilst they are absent on jury service but many employers do.
If you choose not to the employee can claim a loss of earnings allowance from the court. As their employer you will need to complete a loss of earnings certificate which the employee will have been sent when they receive the notification to do jury service. The allowance is currently £64.95 per day for more than 4 hours spent at court or £32.47 for less than 4 hours. This allowance goes towards loss of earnings and any other costs such as childcare.
However, because the allowance is so low many employers will choose to pay their employees as normal or top up the difference between the allowance and their normal earnings. The top up amount will be calculated after the allowance is deducted from their normal net pay so the top up needs to be "grossed up" to allow for normal tax, NI and pension contributions. This will be able to be done using "net to gross" in your payroll software.
Employers must allow employees time off to do jury service. If you do not the employee can complain to an employment tribunal and if they are dismissed due to their jury service they can claim unfair dismissal.
If the employee's absence would seriously harm your business you will need to provide the employee with a letter explaining why. Jury service can only be delayed once in a 12 month period so you would have to allow them to do jury service if called again during that period.
Jury service usually lasts for 10 days but can last longer. Higher loss of earnings allowances are paid if the jury service lasts longer than 10 days.