Will you lose any income while doing jury service?

This means income from an employer or self-employment. Benefits like Jobseeker's Allowance will not be affected unless you do more than 8 weeks of jury service.
My employer has told me they will pay me and then claim the money back from the court
Expenses and loss of earnings can only be reimbursed to the juror if they've suffered financial loss as a direct result of doing jury service. The court will not pay compensation to third parties like employers. If your employer will pay you, then you cannot make a claim for loss of earnings.