A correctly set up and run tronc can save on NI
Tips, no matter how they received, are taxable income and always subject to income tax. This could be deducted at source or collected through self-assessment of the recipient.
If tips and gratuities are retained by the employer, they are subject to Corporation tax, although there is likely to be new legislation to stop this practice, possibly by April 2020. There may also be VAT if they are include as income of the company.