Dave Plowman wrote:

When looking into this, I was surprised just how much an unauthorised
overdraft could cost these days. Some certainly pay for 'free'
banking now.

Unauthorised overdrafts have always been expensive.

My bank gives a £250 free overdraft, then £1.50/day up to £1200,
followed by £1000 of emergency borrowing for £5/day, it has a £15 buffer
zone where you won't be charged extra between the tiers.

Higher overdraft limit is available for 1.5%/year arrangement fee