If you offer free or subsidised meals at your business premises for your staff, this can be done free of tax and National Insurance, but only if the offer is made to all employees, including directors and part-time workers. If the offer is only made to certain employees, the exemption does not apply and then the cost of every meal represents a chargeable benefit in kind. This must then be reported on the employer year end P11D forms and tax and National Insurance would be due on the cost of providing the food and drink.
It is important to note that the offer has to be available for all employees, but if any staff decline the offer, it does not mean that the exemption is lost. The meals do not have to be given to all employees at the same time, they just all need to have the opportunity to take them. You should therefore consider the different working patterns of your staff and perhaps offer the meals at various times on different days of the week to ensure that all staff are included.
If the meals do not qualify for the exemption, you could, as the employer, offer to settle the tax and National Insurance laibilities on behalf of the staff, however this would increase the cost to you considerably.