spreadsheet for interest on rent arrears?

Rent Arrears

I have a tenant who refuses to pay her monthly rent. S21 repossession proceedings have commenced with a hearing scheduled for early July. Due to legal/procedural delays there are some 9 months arrears that now run into several £000’s. I wish to claim interest on the cumulative arrears (several rental periods each with a different overdue period, 14 day grace period for each rental period then standard 3% pa above current BoE bank rate). Is there a spreadsheet available anywhere which calculates the cumulative arrears plus interest with varying BoE bank rates? This situation must similarly affect many landlords on a regular basis.